OTTR


Line plots across dimensions of each concept
Line plots across concepts
Tables

Table of contents



us-gaap:CommonStockValue

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareDiluted

us-gaap:AllocatedShareBasedCompensationExpense
us-gaap:AwardType
us-gaap:TitleOfIndividual, us-gaap:AwardType

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:CostsAndExpenses

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeTaxExpenseBenefit
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:InterestAndDebtExpense
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:NetIncomeLoss
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:StatementEquityComponents

us-gaap:OperatingIncomeLoss

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherNonoperatingIncomeExpense

us-gaap:RegulatedAndUnregulatedOperatingRevenue
us-gaap:ConsolidationItems
us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax
us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService

us-gaap:Revenues
dei:LegalEntity
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:TypeOfArrangement
us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService

us-gaap:Assets
us-gaap:ConsolidatedEntities
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:LiabilitiesAndStockholdersEquity
us-gaap:ConsolidatedEntities

us-gaap:StockholdersEquity
us-gaap:ConsolidatedEntities
us-gaap:StatementEquityComponents

us-gaap:AssetsCurrent
us-gaap:ConsolidatedEntities

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:AccountsReceivableNetCurrent

us-gaap:InventoryNet

us-gaap:InventoryRawMaterialsAndSupplies

us-gaap:OtherAssetsCurrent
us-gaap:ConsolidatedEntities

us-gaap:AssetsNoncurrent

us-gaap:PropertyPlantAndEquipmentGross
us-gaap:PropertyPlantAndEquipmentByType, us-gaap:PublicUtility
us-gaap:PublicUtility

us-gaap:ConstructionInProgressGross

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
us-gaap:PublicUtility

us-gaap:AmortizationOfIntangibleAssets

us-gaap:PropertyPlantAndEquipmentNet
us-gaap:PublicUtility

us-gaap:LongTermInvestments
us-gaap:ConsolidatedEntities

us-gaap:Goodwill
us-gaap:StatementBusinessSegments

us-gaap:IntangibleAssetsNetExcludingGoodwill

us-gaap:FiniteLivedIntangibleAssetsNet
us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:OperatingLeaseRightOfUseAsset

us-gaap:OtherAssetsNoncurrent
us-gaap:ConsolidatedEntities

us-gaap:EquitySecuritiesFvNi
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

us-gaap:AccountsPayableCurrent

us-gaap:LiabilitiesCurrent
us-gaap:ConsolidatedEntities

us-gaap:LongTermDebtCurrent
us-gaap:ConsolidatedEntities

us-gaap:OperatingLeaseLiabilityCurrent

us-gaap:OtherLiabilitiesCurrent
us-gaap:ConsolidatedEntities

us-gaap:LiabilitiesNoncurrent

us-gaap:LongTermDebt

us-gaap:LongTermDebtNoncurrent
us-gaap:ConsolidatedEntities

us-gaap:DeferredIncomeTaxLiabilitiesNet
us-gaap:RetirementPlanType
us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent

us-gaap:OtherLiabilitiesNoncurrent
us-gaap:ConsolidatedEntities

us-gaap:OperatingLeaseLiabilityNoncurrent

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive

us-gaap:OperatingLeaseLiability

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

us-gaap:StockholdersEquity
us-gaap:ConsolidatedEntities
us-gaap:StatementEquityComponents

us-gaap:CommonStockValue

us-gaap:AdditionalPaidInCapitalCommonStock

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

us-gaap:StockIssuedDuringPeriodValueNewIssues
us-gaap:StatementEquityComponents

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue
us-gaap:StatementEquityComponents

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:DeferredIncomeTaxExpenseBenefit

us-gaap:DepreciationDepletionAndAmortization

us-gaap:IncreaseDecreaseInInventories

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetIncomeLoss
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:StatementEquityComponents

us-gaap:ShareBasedCompensation

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:PaymentsToAcquireProductiveAssets

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:ProceedsFromIssuanceOfLongTermDebt

us-gaap:RepaymentsOfLongTermDebt

us-gaap:PaymentsOfDividends

us-gaap:PaymentsForRepurchaseOfCommonStock

us-gaap:EffectiveIncomeTaxRateContinuingOperations

us-gaap:DeferredTaxLiabilities

us-gaap:DeferredTaxAssetsNet

us-gaap:UnrecognizedTaxBenefits

us-gaap:DeferredTaxAssetsValuationAllowance

us-gaap:UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions

us-gaap:ProceedsFromRepaymentsOfShortTermDebt

ottr:AccountsReceivableAllowanceForCreditLossWriteoffAfterRecovery

ottr:ChangeInChecksWrittenInExcessOfCash
dei:LegalEntity, us-gaap:LitigationCase
ottr:ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms
us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService
dei:LegalEntity, us-gaap:CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProject
ottr:CurrentProjectCapitalizedCost
dei:LegalEntity, us-gaap:CounterpartyName, us-gaap:CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProject
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency
ottr:CurrentReturnOnEquityUsedInTransmissionRates
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanAmortizationOfGainsLossesFromOtherComprehensiveIncome
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanAmortizationOfGainsLossesFromRegulatoryAssets
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanAmortizationOfPriorServiceCostFromOtherComprehensiveIncomeCredit
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanAmortizationOfPriorServiceCostFromRegulatoryAssetsCredit

ottr:EffectiveIncomeTaxRateReconciliationAmortizationOfExcessDeferredTaxes

ottr:EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsuranceAmount

ottr:EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsurancePercent

ottr:EffectiveIncomeTaxRateReconciliationDeductionEquityMethodStockAwards

ottr:EffectiveIncomeTaxRateReconciliationTaxCreditProductionPercent
dei:LegalEntity
ottr:EquityToTotalCapitalizationRatio
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType
ottr:EquityToTotalCapitalizationRatioBasisForReturnOnEquity

ottr:IncomeTaxReconciliationAllowanceForFundsUsedDuringConstruction

ottr:IncomeTaxReconciliationDifferencesReversingInExcessOfFederalRates

ottr:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalAndStateStatutoryIncomeTaxRate

ottr:IncreaseDecreaseInDeferredChargesAndOtherAssets

ottr:IncreaseDecreaseInInterestPayableAndIncomeTaxesReceivablePayableNet

ottr:IncreaseDecreaseInOtherOperatingLiabilitiesAndIncreaseDecreaseInDeferredLiabilities
us-gaap:Range, us-gaap:TitleOfIndividual, us-gaap:AwardType, us-gaap:PlanName
ottr:PercentageOfTargetAmountAsActualPayment
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:TypeOfArrangement
ottr:RateRiderRatePercentageOfBase
dei:LegalEntity, us-gaap:RegulatoryAgency
ottr:ReductionInDepreciableLivesIncreaseInDepreciationExpense

us-gaap:AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease

us-gaap:AllowanceForDoubtfulAccountsReceivableWriteOffs
us-gaap:StatementGeographical, us-gaap:ConcentrationRiskByBenchmark, us-gaap:ConcentrationRiskByType
us-gaap:ConcentrationRiskPercentage1
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanContributionsByEmployer
us-gaap:RetirementPlanType, us-gaap:SubsequentEventType
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanInterestCost
us-gaap:NatureOfExpense, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost
us-gaap:RetirementPlanType
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanServiceCost

us-gaap:DividendsCommonStockCash
us-gaap:StatementEquityComponents

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsEmployeeStockOwnershipPlanDividends

us-gaap:EffectiveIncomeTaxRateReconciliationOtherAdjustments

us-gaap:EffectiveIncomeTaxRateReconciliationTaxCreditsOther

us-gaap:IncomeTaxCreditsAndAdjustments

us-gaap:IncomeTaxReconciliationOtherReconcilingItems

us-gaap:IncomeTaxReconciliationPriorYearIncomeTaxes

us-gaap:IncomeTaxReconciliationTaxCreditsOther

us-gaap:IncomeTaxReconciliationTaxCreditsResearch

us-gaap:IncreaseDecreaseInAccountsPayableAndAccruedLiabilities

us-gaap:IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction

us-gaap:IncreaseDecreaseInOtherOperatingAssets

us-gaap:IncreaseDecreaseInReceivables
us-gaap:AwardType
us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:LongTermPurchaseCommitmentAmount

us-gaap:NetPeriodicDefinedBenefitsExpenseReversalOfExpenseExcludingServiceCostComponent

us-gaap:OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeAvailableforsaleSecuritiesTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax

us-gaap:OtherCostAndExpenseOperating

us-gaap:OtherNoncashIncomeExpense

us-gaap:PaymentsForProceedsFromInvestments

us-gaap:PaymentsOfDebtIssuanceCosts

us-gaap:PaymentsOfStockIssuanceCosts

us-gaap:PaymentsRelatedToTaxWithholdingForShareBasedCompensation

us-gaap:PensionContributions
us-gaap:RetirementPlanType
us-gaap:PrescriptionDrugBenefitEffectOfSubsidyOnNetPeriodicPostretirementBenefitCost1

us-gaap:ProceedsFromIssuanceOfCommonStock
dei:LegalEntity, us-gaap:DebtInstrument
us-gaap:ProceedsFromIssuanceOfDebt

us-gaap:ProceedsFromSaleOfProductiveAssets

us-gaap:ProvisionForDoubtfulAccounts
dei:LegalEntity, us-gaap:Range, us-gaap:RegulatoryAgency
us-gaap:PublicUtilitiesRequestedEquityCapitalStructurePercentage
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType
us-gaap:PublicUtilitiesRequestedRateIncreaseDecreaseAmount
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType
us-gaap:PublicUtilitiesRequestedRateIncreaseDecreasePercentage
us-gaap:ConsolidationItems
us-gaap:RegulatedOperatingRevenueElectricNonNuclear
us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:RevenueNotFromContractWithCustomer
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
us-gaap:TitleOfIndividual, us-gaap:AwardType, us-gaap:PlanName, us-gaap:Vesting
us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue
us-gaap:StatementEquityComponents

us-gaap:UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions

us-gaap:UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities

us-gaap:UtilitiesOperatingExpenseFuelUsed

us-gaap:UtilitiesOperatingExpenseMaintenanceAndOperations

us-gaap:UtilitiesOperatingExpenseOther

us-gaap:UtilitiesOperatingExpenseProductsAndServices

us-gaap:UtilitiesOperatingExpensePurchasedPower
us-gaap:ProductOrService

us-gaap:WeightedAverageNumberDilutedSharesOutstandingAdjustment

ottr:AccountsPayableOutstandingRelatedToCapitalAdditions
dei:LegalEntity, us-gaap:DebtInstrument
ottr:DebtInstrumentPrepaymentMinimumPercentageOfAggregatePrincipalAmount
dei:LegalEntity, us-gaap:StatementScenario, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency
ottr:DeferredAndProjectedTransmissionCostsSubjectToFutureRecovery

ottr:DeferredTaxAssetsCostOfRemoval

ottr:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensionAndPostretirementBenefits

ottr:DeferredTaxLiabilitiesExcessTaxOverBookPension

ottr:DeferredTaxLiabilitiesRetirementBenefitsRegulatoryAsset
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanRegulatoryAssets
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanRegulatoryAssetsNetGainsLosses
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanRegulatoryAssetsNetPriorServiceCostCredit
us-gaap:RetirementPlanType
ottr:DefinedBenefitPlanUnrecognizedActuarialGainLoss
dei:LegalEntity, us-gaap:RegulatoryAgency
ottr:EstimatedLiabilityOfRefundObligation
dei:LegalEntity, us-gaap:DebtInstrument
ottr:InterestBearingDebtMaximumPercentageOfTotalCapitalization
us-gaap:JointlyOwnedUtilityPlant
ottr:JointlyOwnedUtilityPlantOwnershipAmountOrDeficitOfConstructionWorkInProgress
dei:LegalEntity
ottr:LandEasementNonleasePaymentsDueTotal
dei:LegalEntity
ottr:LandEasementPaymentsToBePaidAfterYearFive
dei:LegalEntity
ottr:LandEasementPaymentsToBePaidYearFive
dei:LegalEntity
ottr:LandEasementPaymentsToBePaidYearFour
dei:LegalEntity
ottr:LandEasementPaymentsToBePaidYearOne
dei:LegalEntity
ottr:LandEasementPaymentsToBePaidYearThree
dei:LegalEntity
ottr:LandEasementPaymentsToBePaidYearTwo

ottr:LineOfCreditFacilityAmountRestricted
us-gaap:DebtInstrument
us-gaap:DebtInstrument
ottr:LineOfCreditFacilityIncreasedCurrentBorrowingCapacityAccordionProvision
dei:LegalEntity, us-gaap:LitigationCase
ottr:MISOIncentiveROE
dei:LegalEntity
ottr:NetAssetsRestrictedFromDistribution
dei:LegalEntity, us-gaap:RegulatoryAgency

ottr:NetRegulatoryAssetsLiabilityCurrent

ottr:NetRegulatoryAssetsLiabilityNoncurrent

ottr:OtherContractsWithCustomerLiabilityNoncurrent
dei:LegalEntity, us-gaap:RegulatoryAgency
ottr:Ottr_EstimatedLiabilityForFERCOrderedMISOTariffRefundObligation
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType
ottr:PercentageOfRequestedAllowedRateOfReturnOnEquity
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType
ottr:PercentageOfTheRequestedAllowedRateOfReturnOnRateBase
dei:LegalEntity, us-gaap:DebtInstrument
ottr:PriorityDebtToTotalCapitalization

ottr:PublicUtilitiesPropertyPlantAndEquipmentElectric

ottr:TotalDeferredCreditsAndLiabilities
dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:AccountsPayableRelatedPartiesCurrent
us-gaap:ConsolidatedEntities

us-gaap:AccountsReceivableGross

us-gaap:AccountsReceivableGrossCurrent

us-gaap:AccountsReceivableNet
us-gaap:ConsolidatedEntities
dei:LegalEntity
us-gaap:AccountsReceivableRelatedPartiesCurrent
dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:ConsolidatedEntities

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent

us-gaap:AccumulatedDeferredInvestmentTaxCredit

us-gaap:AllowanceForDoubtfulAccountsReceivable
us-gaap:StatementEquityComponents
us-gaap:AociBeforeTaxAttributableToParent
us-gaap:StatementEquityComponents
us-gaap:AociTaxAttributableToParent

us-gaap:AssetRetirementObligation
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
us-gaap:AssetsFairValueDisclosure

us-gaap:AvailableForSaleSecuritiesDebtSecurities
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency, us-gaap:FinancialInstrument

us-gaap:CapitalizationLongtermDebtAndEquity
us-gaap:ConsolidatedEntities
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency
us-gaap:CashAndCashEquivalentsFairValueDisclosure
us-gaap:FairValueByMeasurementBasis

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations
dei:LegalEntity, us-gaap:RegulatoryAgency
us-gaap:ContractWithCustomerLiability
dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency
us-gaap:ContractWithCustomerRefundLiability

us-gaap:DebtInstrumentUnamortizedDiscount
us-gaap:ConsolidatedEntities

us-gaap:DebtLongtermAndShorttermCombinedAmount
us-gaap:ConsolidatedEntities

us-gaap:DebtWeightedAverageInterestRate
us-gaap:ConsolidatedEntities
us-gaap:DeferredIncomeTaxAssetsNet

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards

us-gaap:DeferredTaxAssetsOther

us-gaap:DeferredTaxAssetsPropertyPlantAndEquipment

us-gaap:DeferredTaxAssetsRegulatoryAssetsAndLiabilities

us-gaap:DeferredTaxAssetsTaxCreditCarryforwardsOther

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits

us-gaap:DeferredTaxLiabilitiesOther

us-gaap:DeferredTaxLiabilitiesPropertyPlantAndEquipment

us-gaap:DefinedBenefitPensionPlanLiabilitiesNoncurrent
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedBenefitObligation
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
us-gaap:TitleOfIndividual, us-gaap:RetirementPlanType
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanBenefitObligation
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanFairValueOfPlanAssets
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:RetirementPlanType
us-gaap:RetirementPlanType
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanFundedStatusOfPlan
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear
us-gaap:Range, us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:RetirementPlanFundingStatus, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanUltimateHealthCareCostTrendRate1
us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanWeightedAverageAssetAllocations
us-gaap:RetirementPlanType

us-gaap:EmployeeRelatedLiabilitiesCurrent

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
us-gaap:AwardType

us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization
us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear

us-gaap:FiniteLivedIntangibleAssetsAmortizationExpenseYearFive

us-gaap:FiniteLivedIntangibleAssetsGross
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:InterestReceivableCurrent

us-gaap:InventoryFinishedGoodsNetOfReserves

us-gaap:InventoryWorkInProcess

us-gaap:Investments
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency, us-gaap:InvestmentType
us-gaap:InvestmentsFairValueDisclosure
us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService
us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantNetOwnershipAmount
us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation
dei:LegalEntity, us-gaap:JointlyOwnedUtilityPlant
us-gaap:JointlyOwnedUtilityPlantProportionateOwnershipShare

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths

us-gaap:LettersOfCreditOutstandingAmount
us-gaap:DebtInstrument

us-gaap:LifeInsuranceCorporateOrBankOwnedAmount

us-gaap:LineOfCredit
us-gaap:DebtInstrument

us-gaap:LineOfCreditFacilityMaximumBorrowingCapacity
us-gaap:CreditFacility, us-gaap:DebtInstrument
us-gaap:DebtInstrument

us-gaap:LineOfCreditFacilityRemainingBorrowingCapacity
us-gaap:DebtInstrument
us-gaap:FairValueByMeasurementBasis
us-gaap:LongTermDebtFairValue

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo

us-gaap:MoneyMarketFundsAtCarryingValue

us-gaap:NetRegulatoryAssets
dei:LegalEntity
us-gaap:NotesPayableRelatedPartiesClassifiedCurrent
dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:ConsolidatedEntities
dei:LegalEntity
us-gaap:NotesReceivableRelatedPartiesNoncurrent
dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:ConsolidatedEntities

us-gaap:OperatingLeaseWeightedAverageDiscountRatePercent
us-gaap:IncomeTaxAuthority
us-gaap:OperatingLossCarryforwards
us-gaap:IncomeTaxAuthority, us-gaap:TaxPeriod
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency, us-gaap:InvestmentType
us-gaap:OtherAssetsFairValueDisclosure
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:OtherCommitment

us-gaap:OtherInvestments
us-gaap:RetirementPlanType
us-gaap:OtherPostretirementDefinedBenefitPlanLiabilitiesCurrentAndNoncurrent

us-gaap:OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent

us-gaap:OtherReceivablesGrossCurrent

us-gaap:OtherReceivablesNetCurrent
us-gaap:StatementClassOfStock
us-gaap:PreferredStockSharesOutstanding

us-gaap:PropertyPlantAndEquipmentOther

us-gaap:RegulatoryAssets
us-gaap:ConsolidatedEntities
us-gaap:RegulatoryAsset

us-gaap:RegulatoryAssetsCurrent
us-gaap:RegulatoryAsset

us-gaap:RegulatoryAssetsNoncurrent
us-gaap:RegulatoryAsset

us-gaap:RegulatoryLiabilities
us-gaap:RegulatoryLiability

us-gaap:RegulatoryLiabilityCurrent
us-gaap:RegulatoryLiability

us-gaap:RegulatoryLiabilityNoncurrent
us-gaap:RegulatoryLiability
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue

us-gaap:ShortTermBorrowings
us-gaap:ConsolidatedEntities
us-gaap:DebtInstrument
us-gaap:FairValueByMeasurementBasis
us-gaap:ShorttermDebtFairValue
us-gaap:IncomeTaxAuthority
us-gaap:TaxCreditCarryforwardAmount
us-gaap:IncomeTaxAuthority, us-gaap:TaxPeriod

us-gaap:UnbilledReceivablesCurrent
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears
us-gaap:ConsolidatedEntities, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:ValuationAllowancesAndReservesType
us-gaap:ValuationAllowancesAndReservesBalance
dei:LegalEntity, us-gaap:ConsolidatedEntities, us-gaap:TypeOfArrangement
us-gaap:VariableInterestEntityEntityMaximumLossExposureAmount
us-gaap:InvestmentsByConsolidatedAndNonconsolidatedEntities

Plots across concepts


IncomeStatement
Other Comprehensive Income Loss Net Of Tax
Expenses
Other Nonoperating Income Expense
Balance Sheet
Cash And Cash Equivalents At Carrying Value
Assets
Cash And Cash Equivalents At Carrying Value
Current Assets
Cash And Cash Equivalents At Carrying Value
NonCurrent Assets
Intangible Assets Net Excluding Goodwill
PropertyPlantAndEquipmentNet
Accumulated Depreciation Depletion And Amortization Property Plant And Equipment
Liabilities
Operating Lease Liability
Current Liabilities
Operating Lease Liability Current
Noncurrent Liabilities
Operating Lease Liability Noncurrent
Stockholders Equity
Accumulated Other Comprehensive Income Loss Net Of Tax
CashFlow
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInOperatingActivities
Increase Decrease In Inventories
NetCashProvidedByUsedInInvestingActivities
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInFinancingActivities
Proceeds From Issuance Of Long Term Debt
Shares
Weighted Average Number Of Shares Outstanding Basic
DividendsAndRepurchase
Payments For Repurchase Of Common Stock
OperatingLeaseLiability
Operating Lease Liability Current
LesseeOperatingLeaseLiabilityPaymentsDue
Lessee Operating Lease Liability Undiscounted Excess Amount
FiniteLivedIntangibleAssets
Finite Lived Intangible Assets Net
InventoryNet
Inventory Finished Goods Net Of Reserves
AccountsReceivable
Accounts Receivable Net Current

Tables

  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:CommonStockValue █▇▅▄▂▂▁▁▁▁205.261204.244201.882200.788198.776198.775198.649198.324198.324198.257NA197.787197.787197.775
us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding NA40.67676140.444336NA39.94673939.91783139.903165NA39.90356539.87906939.863682NA39.79536639.702499
us-gaap:WeightedAverageNumberOfSharesOutstandingBasic NA40.51328640.217141NA39.71467239.71203639.657321NA39.62152439.60571739.550874NA39.50758139.462865
us-gaap:EarningsPerShareBasic NA0.420.60.510.620.390.660.36000000000000010.590.470.660.470.450.43
us-gaap:EarningsPerShareDiluted NA0.420.60.50.620.390.660.35000000000000010.580.470.660.459999999999999960.450.42
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
 TTM Greenblatt ROC _ _█▂▅▃▄▂▅▁▅▃▄▃▃▂52.72927.90939.28931.23737.25526.81939.56923.40738.26230.10537.61532.13531.60929.589
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:AllocatedShareBasedCompensationExpense ▁▁█1.2751.2372.77NA1.3012.1481.796NA1.1491.1071.146NA0.8450.77
us-gaap:ComprehensiveIncomeNetOfTax █▂▄▂▄▁▅▁▄▂▄▁▂▁36.00917.1824.47118.41124.86415.57126.49215.82423.43718.85825.71316.1717.86116.887
us-gaap:CostsAndExpenses ▄▁▆▄▅▇█▇▅▆█▃▄▄183.026164.847195.458184.439191.397202.384206.403197.764189.4196.243203.651174.555184.848182.497
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest █▂▅▃▄▂▅▁▅▃▅▄▃▃45.03120.78929.90623.88629.68118.76931.95214.54230.63221.7530.00925.84824.80822.614
us-gaap:IncomeTaxExpenseBenefit █▄▅▄▅▃▅▁▇▃▄▇▆▅9.0973.8085.6383.5344.9363.3435.6280.3817.3593.0543.7947.7487.0355.897
us-gaap:InterestAndDebtExpense ██▅▆▃▄▄▄▃▃▂▁▂▂8.5688.6628.1238.2217.5397.8257.8267.8117.5497.6767.3727.2227.3937.527
us-gaap:NetIncomeLoss █▂▄▃▄▁▅▁▄▂▅▂▂▂35.93416.98124.26820.35224.74515.42626.32414.16123.27318.69626.21518.34217.73416.778
us-gaap:OperatingIncomeLoss █▂▅▃▄▂▅▁▅▃▄▃▃▂52.72927.90939.28931.23737.25526.81939.56923.40738.26230.10537.61532.13531.60929.589
us-gaap:OtherComprehensiveIncomeLossNetOfTax ▅▅▅▁▅▅▅█▅▅▄▁▅▅0.0750.1990.203-1.9410.1190.1450.1681.6630.1640.162-0.502-2.1720.1270.109
us-gaap:OtherNonoperatingIncomeExpense ▆█▁▇▅▄▅▃▅▄▅▄▃▃1.7122.41-0.3891.9981.020.851.2440.3261.2450.7071.1830.9350.5920.552
us-gaap:RegulatedAndUnregulatedOperatingRevenue ▇▁▇▄▆▆█▅▆▅▇▃▄▄235.755192.756234.747215.676228.652229.203245.972221.171227.662226.348241.266206.69216.457212.086
 us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConsolidationItems us-gaap:OperatingSegmentsNANA234.834NANANANANANANANANANANA
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ottr:MetalPartsAndTooling,ottr:Manufacturing▄▁▆▄▆▇█▅▅▆▆▃▃▄50.95737.26757.21150.51256.25562.54166.72453.58655.86457.38856.92746.96444.7549.45
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ottr:PlasticProducts,ottr:Manufacturing▂▂▇▄▃▆▅▅▄▂█▅▂▁7.67.849.8838.6878.0889.3539.0458.858.797.96110.2359.1067.9057.376
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ottr:Wholesale,ottr:Electric▃▁▁▁▄▂▄▃█▇▂▄▄▂1.50.7650.8760.9081.6310.9411.5271.3552.8262.5391.0151.5731.5491.184
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,us-gaap:ElectricTransmission,ottr:Electric█▅▆▁▇▇▆▆█▇▇12.2889.67310.8416.51911.69211.46910.86211.16212.56911.31311.903NANANA
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,us-gaap:ManufacturedProductOther,ottr:Manufacturing▃▁▃▁▃▄▅▆▆█▃▄▄▇1.2920.8411.3850.9651.3791.6022.0532.132.3732.8051.51.5921.72.478
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,us-gaap:ProductAndServiceOther,ottr:Electric▅█▂█▂▁▄▆▂▇▄1.832.1621.5562.1411.6261.4891.8141.9281.6142.0381.742NANANA
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:ProductOrService,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,us-gaap:Retail,ottr:Electric▄▁▆▅▅▂█▅▂▂▇▃▂▁96.82785.344106.69102.17100.34587.976114.955101.3688.7589.4109.1895.28788.48286.679
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ottr:Manufacturing▄▁▆▄▅▇█▅▆▆▆▄▃▄59.84945.94868.47960.16465.72273.49677.82264.56667.02768.15468.66257.66254.35559.304
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ottr:Plastics█▄▃▂▄▆▁▁▆▆▅▁▇▅60.69348.67946.39741.15748.56653.47640.05838.50855.20354.47649.65338.71658.70850.551
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ProductOrService us-gaap:Electricity▄▁▆▄▅▂█▅▃▃▇▄▂▂112.43597.921119.957111.725115.285101.861129.144115.779105.749105.284123.825111.117102.923102.655
 us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ProductOrService us-gaap:Product▇▁▅▂▅█▆▃▇▇▆▁▅▄120.54294.626114.877101.318114.288126.973117.877103.074122.23122.629118.31696.352113.063109.855
us-gaap:Revenues ▇▁▇▄▆▆█▅▆▅▇▃▄▄235.755192.756234.747215.676228.652229.203245.972221.171227.662226.348241.266206.69216.457212.086
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:Assets █▆▅▅▃▂▂▂▁▁2534.5072389.2392306.0022273.5952180.1912114.9442104.5482052.5172027.4162011.247NA2004.2781966.8971944.056
us-gaap:LiabilitiesAndStockholdersEquity █▆▅▅▃▂▂▂▁▁2534.5072389.2392306.0022273.5952180.1912114.9442104.5482052.5172027.4162011.247NA2004.2781966.8971944.056
us-gaap:StockholdersEquity █▇▆▅▄▃▃▃▃▂▂▁▁▁852.07822.055800.019781.482756.505744.305740.499728.863725.302714.581708.05696.892692.519686.404
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:AssetsCurrent █▆▄▄▁▆█▂▂▁274.916266.923256.184254.86237.659263.566273.701241.42241.413239.241NA239.127228.2220.643
us-gaap:CashAndCashEquivalentsAtCarryingValue █▇▂▄▁▁▁▁▁▁▁▃▁44.90439.5127.88421.1990.9210.9820.8910.8610.6491.0361.12116.2160.826NA
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents NANA7.88421.199NANANA0.861NANANA16.216NANA
us-gaap:AccountsReceivableNetCurrent ▆▃▅▂▄▇█▁▅▄100.42384.19796.15877.94792.189105.407113.14475.14496.09591.78NA68.46687.5179.029
us-gaap:InventoryNet ▁▃▆▅▅███▅▃81.87189.75498.15297.85197.052105.86106.732106.2794.61590.435NA88.03478.91587.267
us-gaap:InventoryRawMaterialsAndSupplies ▃▄▇▄▃█▅▃▁▁48.4949.14652.34549.4848.56753.74750.45848.74746.58446.295NA47.20745.5348.644
us-gaap:OtherAssetsCurrent ▅▅▄▁▄▆█▃▆▇7.5528.0317.3475.0426.9268.5119.9866.1148.6119.574NA12.49116.71514.352
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:AssetsNoncurrent NANANA2018.735NANANANANANANANANANA
us-gaap:PropertyPlantAndEquipmentGross █▆▅▄▃▂▂▂▁▁2932.3932785.6362697.7092645.4782570.1132477.5732440.512429.4672409.332385.433NA2339.0222306.4342274.303
us-gaap:ConstructionInProgressGross █▆▄▃▃▁▁▃▃▃454.128321.621234.025185.238141.83973.06949.054181.626183.397168.372NA141.067138.9188.45
us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment █▇▆▅▄▄▃▂▂▁939.59923.948908.337891.684877.958875.475861.401848.369844.042832.873NA799.419785.667773.741
us-gaap:AmortizationOfIntangibleAssets ▁▂▂▃▂▂▂▂▆███▇▇0.2840.2910.2960.2980.2960.2960.2960.2960.3290.3450.3450.3460.3360.333
us-gaap:PropertyPlantAndEquipmentNet █▆▅▄▃▂▁▁▁▁1992.8031861.6881789.3721753.7941692.1551602.0981579.1091581.0981565.2881552.56NA1539.6031520.7671500.562
us-gaap:LongTermInvestments █▇▄▅▅▄▃▂▃▁10.79110.5819.4629.8949.7439.6839.228.9619.1238.649NA8.6298.5998.156
us-gaap:Goodwill ▄▄▄▄▄▄▄▄▄▄37.57237.57237.57237.57237.57237.57237.57237.57237.57237.572NA37.57237.57237.572
us-gaap:IntangibleAssetsNetExcludingGoodwill ▁▂▃▃▄▅▆▆▇█10.41910.70310.99311.2911.56211.85812.15412.4512.74613.075NA13.76514.09714.391
us-gaap:FiniteLivedIntangibleAssetsNet ▁▂▃▃▄▅▆▆▇█10.41910.70310.99311.2911.56211.85812.15412.4512.74613.075NA13.76514.09714.391
us-gaap:OperatingLeaseRightOfUseAsset ▇████▇█▁19.71320.57121.43321.85121.95319.47320.7120.0NANANANANANA
us-gaap:OtherAssetsNoncurrent █▆▄▆▄▄▄▁▂▂42.31640.13838.25240.19638.99639.00238.65335.75936.72136.519NA36.00634.99235.253
us-gaap:EquitySecuritiesFvNi NANANA1.586NANANANANANANANANANA
 us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByFairValueHierarchyLevel,us-gaap:FairValueByMeasurementFrequency us-gaap:FairValueInputsLevel1,us-gaap:FairValueMeasurementsRecurringNANANA1.586NANANANANANANANANANA
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:AccountsPayableCurrent █▄▂▃▁▃▂▁▁▁189.327133.96799.501120.77589.36111.848100.49696.29191.03395.082NA84.18596.21794.353
us-gaap:LiabilitiesCurrent █▅▂▂▆▃▃▁▁▁299.736232.923175.688189.741253.187206.149200.721170.093163.453166.235NA256.653246.176236.994
us-gaap:LongTermDebtCurrent ▃▆█▂▂▂▁▁▁▁0.2150.2610.3060.1830.180.1770.1740.1720.1690.167NA0.1860.19742.2
us-gaap:OperatingLeaseLiabilityCurrent ██▇▇▇▇▇▁4.5814.5434.1974.1364.0063.7843.90.0NANANANANANA
us-gaap:OtherLiabilitiesCurrent ▃▆▃▆▁▆▃▇▄█8.92710.8068.86410.9127.40911.268.57512.1499.37312.665NA11.38914.415.142
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:LiabilitiesNoncurrent NANANA612.791NANANANANANANANANANA
us-gaap:LongTermDebt █▆▆▅▁▁▁▁▁▁767.215727.261727.306692.351592.394592.438592.48592.523592.564592.604NA492.711492.77534.828
us-gaap:LongTermDebtNoncurrent █▆▆▅▁▁▁▁▁▁764.274724.389724.318689.581590.015590.063590.022590.002589.984589.96NA490.38490.406490.386
us-gaap:DeferredIncomeTaxLiabilitiesNet █▄▃▁152.448141.538137.816131.941NANANA120.976NANANANANANA
 us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap:RetirementPlanType us-gaap:PensionPlansDefinedBenefitNANANA55.004NANANA58.659NANANA67.399NANA
us-gaap:OtherLiabilitiesNoncurrent ██▅▅▃▄▂▁▂▁35.14634.64730.91230.83328.1328.85926.35424.32625.88925.06NA22.76922.92122.441
us-gaap:OperatingLeaseLiabilityNoncurrent ▇▇███▇█▁15.77816.58417.75518.19318.38416.08417.160.0NANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo NANANA4.9454.9984.9875.063NANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree NANANA3.9144.7194.74.748NANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour NANANA3.5713.6973.6723.736NANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive NANANA3.0873.3993.373.405NANANANANANANA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive NANANA5.5878.4278.4698.47NANANANANANANA
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:StockholdersEquity █▇▆▅▄▃▃▃▃▂▂▁▁▁852.07822.055800.019781.482756.505744.305740.499728.863725.302714.581708.05696.892692.519686.404
us-gaap:CommonStockValue █▇▅▄▂▂▁▁▁▁205.261204.244201.882200.788198.776198.775198.649198.324198.324198.257NA197.787197.787197.775
us-gaap:AdditionalPaidInCapitalCommonStock █▇▅▄▁▁▁▁▁▁398.301390.141372.669364.79346.294345.03342.991344.25343.21342.69NA343.45342.573341.657
us-gaap:RetainedEarningsAccumulatedDeficit █▆▆▅▄▃▃▂▂▁254.468233.705231.702222.341215.931205.115203.619190.433189.575179.605NA161.286155.618150.558
us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax ▂▂▂▁▇▇▆█▃▂-5.96-6.035-6.234-6.437-4.496-4.615-4.76-4.144-5.807-5.971NA-5.631-3.459-3.586
us-gaap:StockIssuedDuringPeriodValueNewIssues ▄█▄█▁▁7.90218.5978.27519.795-0.0360.017NA0.00.0-0.093NA0.00.0832.322
us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue ▃▃█▁▃▆▅▂▂▂▂▂▁▁1.2751.2372.770.7131.3012.1481.7961.0391.1491.1071.1460.8770.8450.77
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:NetCashProvidedByUsedInOperatingActivities ▇▅▃█▄▅▂▅▅▅▁▆▅▅67.37552.12421.77779.88835.86252.13717.1542.58847.46548.7554.6459.544.80548.071
us-gaap:NetCashProvidedByUsedInInvestingActivities ▁▆▃▅▂▇█▇███▇▇█-101.38-45.946-75.059-58.342-95.747-29.947-25.436-31.485-26.215-25.892-23.827-37.339-38.633-26.609
us-gaap:NetCashProvidedByUsedInFinancingActivities ▆▅▆▃█▁▄▂▁▁▃▂▂▁39.39725.4539.967-1.26859.824-22.0998.316-10.891-21.637-22.9484.092-6.771-5.346-21.462
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect ▄█▁▆▃5.39231.628-13.31520.278-0.061NANANANANANANANANA
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:DeferredIncomeTaxExpenseBenefit █▄▅▆▃▂▂█▅▁▃▆▅▄10.8813.665.8128.022.5270.1250.83511.6955.453-0.8252.9018.3217.0144.154
us-gaap:DepreciationDepletionAndAmortization ███▆▆▅▄▃▃▃▃▄▁▁20.39520.43620.39919.85719.65719.44119.13118.4518.70818.74518.76318.85617.92717.908
us-gaap:IncreaseDecreaseInInventories ▁▁▄▄▁▄▄█▅▅▄▇▁▆-7.883-8.3980.3010.799-8.808-0.8720.46211.6554.182.436-0.0359.119-8.3525.794
us-gaap:NetCashProvidedByUsedInOperatingActivities ▇▅▃█▄▅▂▅▅▅▁▆▅▅67.37552.12421.77779.88835.86252.13717.1542.58847.46548.7554.6459.544.80548.071
us-gaap:NetIncomeLoss █▂▄▃▄▁▅▁▄▂▅▂▂▂35.93416.98124.26820.35224.74515.42626.32414.16123.27318.69626.21518.34217.73416.778
us-gaap:ShareBasedCompensation ▃▃█▁▃▆▅▂▂▂▂▂▁▁1.2751.2372.770.7131.3012.1481.7961.0391.1491.1071.1460.8770.8450.77
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:NetCashProvidedByUsedInInvestingActivities ▁▆▃▅▂▇█▇███▇▇█-101.38-45.946-75.059-58.342-95.747-29.947-25.436-31.485-26.215-25.892-23.827-37.339-38.633-26.609
us-gaap:PaymentsToAcquireProductiveAssets █▃▆▄█▂▁▂▁▁▁▂▂▁100.844.77175.05957.6795.68329.32524.68730.93625.39525.47623.61838.36438.19526.241
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
us-gaap:NetCashProvidedByUsedInFinancingActivities ▆▅▆▃█▁▄▂▁▁▃▂▂▁39.39725.4539.967-1.26859.824-22.0998.316-10.891-21.637-22.9484.092-6.771-5.346-21.462
us-gaap:ProceedsFromIssuanceOfLongTermDebt ▄▁▃█▁▁▁▁▁▁█40.00.035.0100.00.00.00.00.00.00.0100.0NANANA
us-gaap:RepaymentsOfLongTermDebt ▁▁▁▁▁▁▁▁▁▁▁▁█▂0.0460.0450.0450.0440.0440.0420.0420.0410.0410.0470.060.05942.0583.057
us-gaap:PaymentsOfDividends █▇▇▃▃▃▃▁▁▁▁15.17114.97814.90713.94213.92913.9313.92213.30313.30313.313.292NANANA
us-gaap:PaymentsForRepurchaseOfCommonStock NANA2.072NANA0.02.73-0.0010.5620.0412.4090.00.00.04
  2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue


Common
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value207207205204201200198198198198198198197197197197196196193190189188187187186183183181181181180180180180180180180180
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets7.98.08.18.58.88.89.19.49.49.79.89.99.910.110.210.210.310.510.410.410.410.210.410.310.410.710.911.410.911.411.311.511.110.810.610.510.610.2

Weighted Average Number Of Diluted Shares Outstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding


Weighted
Period End2021-03-312020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value4140403939393939393939393938383737373636363636363636361293617136163360813607635799
Percentage of WeightedAverageNumberOfDilutedSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Weighted Average Number Of Shares Outstanding Basic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic


Weighted
Period End2021-03-312020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value4140403939393939393939393838373737373636363636363636359953593335926358763580635799
Percentage of WeightedAverageNumberOfSharesOutstandingBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareBasic


Earnings
Period End2021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value0.730.420.60.510.620.390.660.360.590.470.660.470.450.430.50.450.380.410.380.380.410.310.480.280.430.270.590.420.210.410.05-0.490.2-1.240.170.510.150.050.17-0.4
Percentage of EarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted

us-gaap:EarningsPerShareDiluted


Earnings
Period End2021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value0.730.420.60.50.620.390.660.350.580.470.660.460.450.420.490.440.370.410.380.390.410.30.480.280.430.270.590.420.210.410.05-0.490.2-1.230.170.510.150.050.16-0.4
Percentage of EarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Allocated Share Based Compensation Expense

us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:AllocatedShareBasedCompensationExpense


Allocated
Period End2021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value4.21.2751.2372.771.3012.1481.7961.1491.1071.1460.8450.771.150.7780.6431.0260.160.541.643-0.0530.8960.8840.6771.0981.4890.4630.6180.2872.6050.470.4521.1530.424
Percentage of AllocatedShareBasedCompensationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.50.61.20.60.90.70.50.50.50.40.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AllocatedShareBasedCompensationExpense us-gaap:AwardType

ottr:EmployeeStockPurchasePlan


Allocated
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-30
Value0.0410.0420.0530.0540.00.00.0
Percentage of AllocatedShareBasedCompensationExpense3.23.41.94.20.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:EmployeeStockPurchasePlan0.00.00.00.00.00.00.0

us-gaap:AllocatedShareBasedCompensationExpense us-gaap:TitleOfIndividual, us-gaap:AwardType

ottr:ExecutiveOfficersAndKeyEmployees, us-gaap:RestrictedStockUnitsRSU


Allocated
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value0.1060.1060.6790.1890.3830.427
Percentage of AllocatedShareBasedCompensationExpense8.38.624.514.517.823.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.10.30.10.20.2
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:ExecutiveOfficersAndKeyEmployees us-gaap:RestrictedStockUnitsRSU0.00.00.00.00.00.0

ottr:NonExecutiveEmployees, us-gaap:RestrictedStockUnitsRSU


Allocated
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value0.1330.1410.1340.1120.1430.091
Percentage of AllocatedShareBasedCompensationExpense10.411.44.88.66.75.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.10.10.10.00.10.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:NonExecutiveEmployees us-gaap:RestrictedStockUnitsRSU0.00.00.00.00.00.0

ottr:NonemployeeDirectors, us-gaap:RestrictedStockUnitsRSU


Allocated
Period End2020-09-302020-06-302019-09-302019-06-30
Value0.2370.2360.2030.204
Percentage of AllocatedShareBasedCompensationExpense18.619.115.69.5
Percentage of RegulatedAndUnregulatedOperatingRevenue0.10.10.10.1
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:NonemployeeDirectors us-gaap:RestrictedStockUnitsRSU0.00.00.00.0

srt:ExecutiveOfficer, ottr:StockPerformanceAwards


Allocated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value0.7580.7121.70.3230.7431.4181.1130.6080.7180.6680.651
Percentage of AllocatedShareBasedCompensationExpense59.557.661.40.057.166.062.00.062.560.356.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.30.40.70.00.30.60.50.00.30.30.3
Percentage of RegulatedAndUnregulatedOperatingRevenue srt:ExecutiveOfficer ottr:StockPerformanceAwards0.00.00.00.00.00.00.00.00.00.00.0

Comprehensive Income Net Of Tax

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTax


Comprehensive
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value301636172418241526152318251617161917141514141511187.472151021157.736151.976-17.2927.367-44.6886.413145.2614.1636.744-14.798
Percentage of ComprehensiveIncomeNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.015.38.910.40.010.96.810.80.010.38.310.70.08.38.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Costs And Expenses

us-gaap:CostsAndExpenses

us-gaap:CostsAndExpenses


Costs
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value21719818316419518419120220619718919620317418418218116716917617815917016317763214216179204196190255307260159298302233125247266
Percentage of CostsAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.077.685.583.30.083.788.383.90.083.286.784.40.085.486.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest


Income
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-31
Value3520452029232918311430213025242225211920192222171711211130199.598211.02-31.3799.7889.7185.046.451
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.019.110.812.70.013.08.213.00.013.59.612.40.011.510.70.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Income Tax Expense Benefit

us-gaap:IncomeTaxExpenseBenefit

us-gaap:IncomeTaxExpenseBenefit


Income
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value5.2491.6639.0973.8085.6383.5344.9363.3435.6280.3817.3593.0543.7947.7487.0355.8976.3634.3435.1635.0835.4927.046.5214.0084.0731.3075.4761.4868.5625.1332.0945.886-0.858-14.4930.297-2.1072.1090.5371.2385.642-0.607-7.769
Percentage of IncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.03.92.02.40.02.21.52.30.03.21.31.60.03.32.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:IncomeTaxExpenseBenefit us-gaap:ConsolidationItems

us-gaap:CorporateNonSegment


Income
Period End2020-12-312020-09-302020-06-302019-12-312019-09-302019-06-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value-1.691-1.48-0.4-1.377-1.329-0.887-0.976-2.144-1.377-1.326-0.89-1.506-0.843-1.301-0.851-1.916-2.396-0.427-2.21-0.992-2.027-1.109-6.405
Percentage of IncomeTaxExpenseBenefit-101.7-16.3-10.5-39.0-26.9-26.5-16.6-33.7-31.7-25.7-17.5-27.4-12.0-20.0-21.2-47.0-183.3-7.8-148.7-11.6-39.5-53.0746.5
Percentage of RegulatedAndUnregulatedOperatingRevenue0.0-0.6-0.20.0-0.6-0.4-0.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:CorporateNonSegment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:IncomeTaxExpenseBenefit us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Income
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value0.2336.0482.5793.622.9934.0661.0374.771-2.1965.1720.6112.0984.9613.5482.4425.1044.731.92
Percentage of IncomeTaxExpenseBenefit14.066.567.764.284.782.431.084.8-576.470.320.055.364.050.441.4117.591.637.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.02.61.31.50.01.80.51.90.02.30.30.90.01.61.20.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Manufacturing


Income
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value0.7760.891-0.1891.461-0.1040.2851.1491.4540.3530.7991.0181.223-2.3150.6761.5731.055-0.7160.1821.7911.019-0.2170.8551.1570.504-0.0541.1641.3361.6711.1241.3731.288
Percentage of IncomeTaxExpenseBenefit46.79.8-5.025.9-2.95.834.425.892.710.933.332.2-29.99.626.716.6-16.53.535.218.6-3.113.128.912.4-4.121.389.919.521.965.6-150.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.4-0.10.60.00.10.50.60.00.40.40.50.00.30.70.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Plastics


Income
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value2.3453.6381.8181.9172.0221.9142.0441.3291.8312.2762.2072.414-0.6263.8262.8581.391.3321.5772.2621.3672.0282.2062.6891.2641.1661.8882.1142.1332.2782.6272.216
Percentage of IncomeTaxExpenseBenefit141.040.047.734.057.238.861.123.6480.630.972.363.6-8.154.448.521.830.730.544.524.928.833.867.131.089.234.5142.324.944.4125.5-258.3
Percentage of RegulatedAndUnregulatedOperatingRevenue0.01.50.90.80.00.80.90.50.01.01.01.00.01.81.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Plastics0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Interest And Debt Expense

us-gaap:InterestAndDebtExpense

us-gaap:InterestAndDebtExpense


Interest
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value9.3989.0948.5688.6628.1238.2217.5397.8257.8267.8117.5497.6767.3727.2227.3937.5277.4627.898.0267.9767.9947.9857.737.7027.7437.7397.6877.6276.5956.5746.8776.987.9048.4778.6168.4728.7089.1499.4769.2339.2879.398
Percentage of InterestAndDebtExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.03.64.53.50.03.33.43.20.03.33.43.10.03.43.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:InterestAndDebtExpense us-gaap:ConsolidationItems

us-gaap:CorporateNonSegment


Interest
Period End2020-12-312020-09-302020-06-302019-12-312019-09-302019-06-30
Value0.6110.5180.5740.5280.4810.339
Percentage of InterestAndDebtExpense6.76.06.66.46.44.3
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.20.30.00.20.1
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:CorporateNonSegment0.00.00.00.00.00.0

us-gaap:InterestAndDebtExpense us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Interest
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value7.7827.3347.3487.3846.9826.36.6256.6416.7796.5096.6876.396.1476.3626.4396.3256.3046.156
Percentage of InterestAndDebtExpense85.685.684.890.984.983.684.784.986.886.287.186.785.186.185.580.278.577.2
Percentage of RegulatedAndUnregulatedOperatingRevenue0.03.13.83.10.02.82.92.70.02.93.02.60.02.93.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Manufacturing


Interest
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value0.5540.5530.5540.5540.5540.5610.6460.5840.5660.5550.5550.5540.5530.5550.5530.5540.8870.9741.0060.9920.9820.90.8460.8320.810.8120.8130.8080.8160.8160.891
Percentage of InterestAndDebtExpense6.16.56.46.86.77.48.37.57.27.47.27.57.77.57.37.411.212.112.612.412.311.611.010.710.510.610.712.312.411.911.3
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.20.30.20.00.20.30.20.00.20.20.20.00.30.30.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Plastics


Interest
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value0.1470.1630.1860.1480.1570.1970.2150.1490.1490.150.160.150.150.1570.1730.1530.2380.2730.2790.2440.2440.2570.2790.2460.2460.2760.2740.2470.2490.2560.342
Percentage of InterestAndDebtExpense1.61.92.11.81.92.62.71.91.92.02.12.02.12.12.32.13.03.43.53.13.13.33.63.23.23.63.63.73.83.74.3
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.10.10.10.00.10.10.10.00.10.10.10.00.10.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Plastics0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value3018351624202415261423182618171619171415141415111710159.99321157.701151.873-17.3567.243-44.1356.368185.6962.0566.101-14.218
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.015.28.810.30.010.86.710.70.010.28.310.90.08.27.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems

us-gaap:CorporateNonSegment


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302017-06-302017-03-312016-06-302016-03-31
Value-1.79-3.117-2.457-1.693-2.29-1.376-1.489-1.858-1.009-0.64-0.086-2.053
Percentage of NetIncomeLoss-5.9-16.7-6.8-10.0-9.4-6.8-6.0-12.0-6.0-3.3-0.5-14.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-1.0-0.9-1.00.0-0.7-0.8-0.50.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:CorporateNonSegment0.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value171224131615177.502181214101612101015129.148
Percentage of NetIncomeLoss58.067.268.878.466.774.571.548.671.088.962.656.763.670.261.360.489.385.658.4
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.010.56.96.90.07.73.37.60.06.44.76.90.05.04.80.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Manufacturing


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value5.3852.5723.3110.2384.9270.9123.1553.994.8422.073.0223.5834.1644.3151.6082.9552.172-0.4141.2463.0091.853
Percentage of NetIncomeLoss17.813.89.21.420.34.512.825.918.414.613.019.215.923.59.117.611.1-2.48.519.212.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.01.40.12.10.01.41.72.00.01.31.61.70.00.71.40.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Plastics


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value9.1476.66105.135.4495.6545.3975.7923.7294.3146.4326.2296.8448.536.0924.6372.4372.6452.3463.4852.152
Percentage of NetIncomeLoss30.235.728.830.222.527.821.837.514.230.527.633.326.146.534.427.612.415.116.122.214.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.04.42.72.30.02.42.51.50.02.82.82.80.02.82.20.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Plastics0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value301835162420241526142318261817161917141514141511171015
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.015.28.810.30.010.86.710.70.010.28.310.90.08.27.90.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Operating Income Loss

us-gaap:OperatingIncomeLoss

us-gaap:OperatingIncomeLoss


Operating
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value442752273931372639233830373231293229272727292924251828183525152721-23.643174.561714151312-15.198
Percentage of OperatingIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.022.414.516.70.016.311.716.10.016.813.315.60.014.614.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Other Comprehensive Income Loss Net Of Tax

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTax


Other
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value75000.0199000.0203000.0-1941000.0119000.0145000.0168000.01663000.0164000.0162000.0-502000.0-2172000.0127000.0109000.0105000.0-224000.072000.0110000.0140000.0397000.0127000.0100000.0141000.0-3003000.06000.054000.08000.099000.035000.068000.0103000.064000.0124000.045000.0-3976000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.10.10.00.10.10.10.00.10.1-0.20.00.10.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Other Nonoperating Income Expense

us-gaap:OtherNonoperatingIncomeExpense

us-gaap:OtherNonoperatingIncomeExpense


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1.162.3221.7122.41-0.3891.9981.020.851.2440.3261.2450.7071.1830.9350.5920.552
Percentage of OtherNonoperatingIncomeExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.71.3-0.20.00.40.40.50.00.50.30.50.00.30.3

Regulated And Unregulated Operating Revenue

us-gaap:RegulatedAndUnregulatedOperatingRevenue

us-gaap:RegulatedAndUnregulatedOperatingRevenue


Regulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value235192234215228229245221227226241206216212
Percentage of RegulatedAndUnregulatedOperatingRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Revenue From Contract With Customer Excluding Assessed Tax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ConsolidationItems

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax

us-gaap:OperatingSegments


Revenue
Period End2021-03-312020-03-31
Value262234
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments0.00.0

Revenue From Contract With Customer Including Assessed Tax

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax

us-gaap:OperatingSegments, ottr:MetalPartsAndTooling, ottr:Manufacturing


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value5037575056626653555756464449
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue21.619.324.423.424.627.327.124.224.525.423.622.720.723.3
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:MetalPartsAndTooling ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:PlasticProducts, ottr:Manufacturing


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value7.67.849.8838.6878.0889.3539.0458.858.797.961109.1067.9057.376
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax14.921.017.317.214.415.013.616.515.713.918.019.417.714.9
Percentage of RegulatedAndUnregulatedOperatingRevenue3.24.14.24.03.54.13.74.03.93.54.24.43.73.5
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:PlasticProducts ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Wholesale, ottr:Electric


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1.50.7650.8760.9081.6310.9411.5271.3552.8262.5391.0151.5731.5491.184
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax2.92.11.51.82.91.52.32.55.14.41.83.33.52.4
Percentage of RegulatedAndUnregulatedOperatingRevenue0.60.40.40.40.70.40.60.61.21.10.40.80.70.6
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Wholesale ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, us-gaap:ElectricTransmission, ottr:Electric


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value129.673106.51911111011121111
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax24.126.018.912.920.818.316.320.822.519.720.9
Percentage of RegulatedAndUnregulatedOperatingRevenue5.25.04.63.05.15.04.45.05.55.04.9
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments us-gaap:ElectricTransmission ottr:Electric0.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, us-gaap:ManufacturedProductOther, ottr:Manufacturing


Revenue
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1.7341.2920.8411.3850.9651.3791.6022.0532.132.3732.8051.51.5921.72.478
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.02.52.32.41.92.52.63.14.04.24.92.63.43.85.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.50.40.60.40.60.70.81.01.01.20.60.80.81.2
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments us-gaap:ManufacturedProductOther ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, us-gaap:ProductAndServiceOther, ottr:Electric


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value1.832.1621.5562.1411.6261.4891.8141.9281.6142.0381.742
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.65.82.74.22.92.42.73.62.93.63.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.81.10.71.00.70.60.70.90.70.90.7
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments us-gaap:ProductAndServiceOther ottr:Electric0.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, us-gaap:Retail, ottr:Electric


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value9685106102100871141018889109958886
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax190.0229.0186.5202.3178.4140.7172.3189.2158.9155.8191.8202.9197.7175.3
Percentage of RegulatedAndUnregulatedOperatingRevenue41.144.345.447.443.938.446.745.839.039.545.346.140.940.9
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments us-gaap:Retail ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Manufacturing


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value5945686065737764676868575459
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax117.5123.3119.7119.1116.8117.5116.6120.5120.0118.8120.6122.8121.5119.9
Percentage of RegulatedAndUnregulatedOperatingRevenue25.423.829.227.928.732.131.629.229.430.128.527.925.128.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Plastics


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value6048464148534038555449385850
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax119.1130.681.181.586.385.560.071.998.894.987.282.4131.2102.2
Percentage of RegulatedAndUnregulatedOperatingRevenue25.725.319.819.121.223.316.317.424.224.120.618.727.123.8
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Plastics0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ProductOrService

us-gaap:Electricity


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value11297119111115101129115105105123111102102
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax220.6262.8209.7221.2204.9162.9193.5216.1189.3183.5217.5236.6230.0207.6
Percentage of RegulatedAndUnregulatedOperatingRevenue47.750.851.151.850.444.452.552.346.546.551.353.847.548.4
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:Electricity0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Product


Revenue
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1209411410111412611710312212211896113109
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax236.6253.9200.8200.6203.2203.0176.7192.4218.8213.7207.8205.2252.7222.2
Percentage of RegulatedAndUnregulatedOperatingRevenue51.149.148.947.050.055.447.946.653.754.249.046.652.251.8
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:Product0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Revenues

us-gaap:Revenues

us-gaap:Revenues


Revenues
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value26122623519223421522822924522122722624120621621221419619720320618820018820281242234214229212217277283277163315316249138259251
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues dei:LegalEntity

ottr:OtterTailPowerCompany


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value117.01610104.3995.3148.145118.3778.51210
Percentage of Revenues4.83.64.34.81.92.33.35.03.73.84.2
Percentage of RegulatedAndUnregulatedOperatingRevenue4.83.64.34.81.92.33.35.03.73.84.2
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany0.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency

ottr:OtterTailPowerCompany, ottr:ConservationImprovementProgramCostsAndIncentives, ottr:Minnesota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value2.0961.5211.0864.0251.5182.6180.8873.8271.4882.368
Percentage of Revenues0.90.80.51.90.71.10.41.70.71.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.90.80.51.90.71.10.41.70.71.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:ConservationImprovementProgramCostsAndIncentives ottr:Minnesota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:ConservationImprovementProgramCostsAndIncentives, ottr:SouthDakota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.1940.210.3440.4110.10.0960.2440.0390.2380.122
Percentage of Revenues0.10.10.10.20.00.00.10.00.10.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.10.10.10.20.00.00.10.00.10.1
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:ConservationImprovementProgramCostsAndIncentives ottr:SouthDakota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:GenerationCostRecovery, ottr:NorthDakota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value1.1870.90.9480.2710.1370.2220.2480.00.00.0
Percentage of Revenues0.50.50.40.10.10.10.10.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.50.50.40.10.10.10.10.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:GenerationCostRecovery ottr:NorthDakota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:PhaseInRatePlan, ottr:SouthDakota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value-0.053-0.670.646-0.115-0.010.00.0
Percentage of Revenues-0.0-0.30.3-0.1-0.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue-0.0-0.30.3-0.1-0.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:PhaseInRatePlan ottr:SouthDakota10.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:Minnesota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.3183.0883.2541.5641.3161.3171.3161.0660.8170.659
Percentage of Revenues1.41.61.40.70.60.60.50.50.40.3
Percentage of RegulatedAndUnregulatedOperatingRevenue1.41.61.40.70.60.60.50.50.40.3
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:Minnesota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value1.2561.071.129-0.386-0.02-0.0930.7292.2632.222.079
Percentage of Revenues0.50.60.5-0.2-0.0-0.00.31.01.00.9
Percentage of RegulatedAndUnregulatedOperatingRevenue0.50.60.5-0.2-0.0-0.00.31.01.00.9
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:NorthDakota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:Minnesota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value2.001-0.3140.7152.196-0.284-0.0560.641-0.356-1.196-0.458
Percentage of Revenues0.8-0.20.31.0-0.1-0.00.3-0.2-0.5-0.2
Percentage of RegulatedAndUnregulatedOperatingRevenue0.8-0.20.31.0-0.1-0.00.3-0.2-0.5-0.2
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:Minnesota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:NorthDakota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.8090.841.4821.7380.9080.8741.7721.8671.9221.165
Percentage of Revenues0.30.40.60.80.40.40.70.80.80.5
Percentage of RegulatedAndUnregulatedOperatingRevenue0.30.40.60.80.40.40.70.80.80.5
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:NorthDakota10.00.00.00.00.00.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:SouthDakota1


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.450.3710.5620.5780.7430.3710.4730.3820.4960.25
Percentage of Revenues0.20.20.20.30.30.20.20.20.20.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.20.20.20.30.30.20.20.20.20.1
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:SouthDakota10.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:TypeOfArrangement

ottr:OtterTailPowerCompany, ottr:ConservationImprovementProgramCostsAndIncentives, ottr:Minnesota1, ottr:The2017IncentiveAndCostRecovery


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.0100.00.0
Percentage of Revenues0.00.04.40.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.04.40.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:ConservationImprovementProgramCostsAndIncentives ottr:Minnesota1 ottr:The2017IncentiveAndCostRecovery0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:ConservationImprovementProgramCostsAndIncentives, ottr:Minnesota1, ottr:The2018IncentiveAndCostRecovery


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.0110.00.0
Percentage of Revenues0.00.05.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.05.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:ConservationImprovementProgramCostsAndIncentives ottr:Minnesota1 ottr:The2018IncentiveAndCostRecovery0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:ConservationImprovementProgramCostsAndIncentives, ottr:Minnesota1, ottr:The2019IncentiveAndCostRecovery


Revenuesdei:
Period End2020-09-302020-06-302020-03-31
Value0.00.08.247
Percentage of Revenues0.00.03.5
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.03.5
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:ConservationImprovementProgramCostsAndIncentives ottr:Minnesota1 ottr:The2019IncentiveAndCostRecovery0.00.00.0

ottr:OtterTailPowerCompany, ottr:EnvironmentalCostRecoveryRider, ottr:NorthDakota1, ottr:The2018AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.0-0.3780.00.0
Percentage of Revenues0.00.0-0.20.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-0.20.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:EnvironmentalCostRecoveryRider ottr:NorthDakota1 ottr:The2018AnnualUpdate0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:EnvironmentalCostRecoveryRider, ottr:NorthDakota1, ottr:The2018RateResetForEffectOfTCJA


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.07.7180.00.0
Percentage of Revenues0.00.03.30.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.03.30.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:EnvironmentalCostRecoveryRider ottr:NorthDakota1 ottr:The2018RateResetForEffectOfTCJA0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:EnvironmentalCostRecoveryRider, ottr:SouthDakota1, ottr:The2018InterimRateReset


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.0-0.1890.00.0
Percentage of Revenues0.00.0-0.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-0.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:EnvironmentalCostRecoveryRider ottr:SouthDakota1 ottr:The2018InterimRateReset0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:GenerationCostRecovery, ottr:NorthDakota1, ottr:The2019InitialRequest


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.02.720.00.0
Percentage of Revenues0.00.01.20.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.01.20.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:GenerationCostRecovery ottr:NorthDakota1 ottr:The2019InitialRequest0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:GenerationCostRecovery, ottr:NorthDakota1, ottr:The2020AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-31
Value0.00.06.184
Percentage of Revenues0.00.02.6
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.02.6
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:GenerationCostRecovery ottr:NorthDakota1 ottr:The2020AnnualUpdate0.00.00.0

ottr:OtterTailPowerCompany, ottr:PhaseInRatePlan, ottr:SouthDakota1, ottr:The2019InitialRequest


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.00.8640.0-0.163
Percentage of Revenues0.00.00.40.0-0.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.40.0-0.1
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:PhaseInRatePlan ottr:SouthDakota1 ottr:The2019InitialRequest0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:PhaseInRatePlanRecovery, ottr:SouthDakota1, ottr:The2020AnnualUpdate


Revenuesdei:
Period End2020-09-30
Value-0.306
Percentage of Revenues-0.1
Percentage of RegulatedAndUnregulatedOperatingRevenue-0.1
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:PhaseInRatePlanRecovery ottr:SouthDakota1 ottr:The2020AnnualUpdate0.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:Minnesota1, ottr:The2018AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.05.8801140.0058860.00.0
Percentage of Revenues0.03.10.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.03.10.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:Minnesota1 ottr:The2018AnnualUpdate0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:Minnesota1, ottr:The2019AnnualUpdateRevised


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-31
Value0.00.0120.0
Percentage of Revenues0.00.05.30.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.05.30.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:Minnesota1 ottr:The2019AnnualUpdateRevised0.00.00.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1, ottr:The2018RateResetForEffectOfTCJA


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.09.650.00.0
Percentage of Revenues0.00.04.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.04.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:NorthDakota1 ottr:The2018RateResetForEffectOfTCJA0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1, ottr:The2019AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.0-0.2350.00.0
Percentage of Revenues0.00.0-0.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-0.10.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:NorthDakota1 ottr:The2019AnnualUpdate0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1, ottr:The2020AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-31
Value0.00.05.762
Percentage of Revenues0.00.02.5
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.02.5
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:RenewableResourceAdjustment ottr:NorthDakota1 ottr:The2020AnnualUpdate0.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:Minnesota1, ottr:The2017RateReset


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.0-3.3110.00.0
Percentage of Revenues0.00.0-1.40.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-1.40.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:Minnesota1 ottr:The2017RateReset0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:Minnesota1, ottr:The2018AnnualUpdate


Revenuesdei:
Period End2020-09-30
Value-0.004
Percentage of Revenues-0.0
Percentage of RegulatedAndUnregulatedOperatingRevenue-0.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:Minnesota1 ottr:The2018AnnualUpdate0.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:NorthDakota1, ottr:The2018RateResetForEffectOfTCJA


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.07.4690.00.0
Percentage of Revenues0.00.03.20.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.03.20.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:NorthDakota1 ottr:The2018RateResetForEffectOfTCJA0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:NorthDakota1, ottr:The2018SupplementalUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.04.8010.00.0
Percentage of Revenues0.00.02.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.02.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:NorthDakota1 ottr:The2018SupplementalUpdate0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:NorthDakota1, ottr:The2019AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-31
Value0.00.05.7390.0
Percentage of Revenues0.00.02.40.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.02.40.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:NorthDakota1 ottr:The2019AnnualUpdate0.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:SouthDakota1, ottr:The2018InterimRateReset


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.01.1710.00.0
Percentage of Revenues0.00.00.50.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.50.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:SouthDakota1 ottr:The2018InterimRateReset0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:SouthDakota1, ottr:The2019AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.01.6380.00.0
Percentage of Revenues0.00.00.70.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.70.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:SouthDakota1 ottr:The2019AnnualUpdate0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:SouthDakota1, ottr:The2019RateReset


Revenuesdei:
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.00.02.0460.0-0.004
Percentage of Revenues0.00.00.90.0-0.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.90.0-0.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:SouthDakota1 ottr:The2019RateReset0.00.00.00.00.0

ottr:OtterTailPowerCompany, ottr:TransmissionCostRecoveryRider, ottr:SouthDakota1, ottr:The2020AnnualUpdate


Revenuesdei:
Period End2020-09-302020-06-302020-03-31
Value0.00.02.327
Percentage of Revenues0.00.01.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.01.0
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:OtterTailPowerCompany ottr:TransmissionCostRecoveryRider ottr:SouthDakota1 ottr:The2020AnnualUpdate0.00.00.0

us-gaap:Revenues us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:ElectricProductOther, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value1.5421.55
Percentage of Revenues0.60.7
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.7
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:ElectricProductOther ottr:Electric0.00.0

us-gaap:OperatingSegments, ottr:ElectronicProductRetail, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value105106
Percentage of Revenues40.445.4
Percentage of RegulatedAndUnregulatedOperatingRevenue0.045.4
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:ElectronicProductRetail ottr:Electric0.00.0

us-gaap:OperatingSegments, ottr:MetalPartsAndTooling, ottr:Manufacturing


Revenuesus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value62545037575056626653555756464449
Percentage of Revenues23.923.821.619.324.423.424.627.327.124.224.525.423.622.720.723.3
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.021.619.324.423.424.627.327.124.224.525.423.622.720.723.3
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:MetalPartsAndTooling ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:PlasticProducts, ottr:Manufacturing


Revenuesus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value108.7327.67.849.8838.6878.0889.3539.0458.858.797.961109.1067.9057.376
Percentage of Revenues3.93.83.24.14.24.03.54.13.74.03.93.54.24.43.73.5
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.03.24.14.24.03.54.13.74.03.93.54.24.43.73.5
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:PlasticProducts ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:RetailCommercialAndIndustrial, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value6668
Percentage of Revenues25.429.4
Percentage of RegulatedAndUnregulatedOperatingRevenue0.029.4
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:RetailCommercialAndIndustrial ottr:Electric0.00.0

us-gaap:OperatingSegments, ottr:RetailOther, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value1.8181.822
Percentage of Revenues0.70.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.8
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:RetailOther ottr:Electric0.00.0

us-gaap:OperatingSegments, ottr:RetailResidential, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value3735
Percentage of Revenues14.315.3
Percentage of RegulatedAndUnregulatedOperatingRevenue0.015.3
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:RetailResidential ottr:Electric0.00.0

us-gaap:OperatingSegments, ottr:ScrapMetalSales, ottr:Manufacturing


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value2.8571.385
Percentage of Revenues1.10.6
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.6
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:ScrapMetalSales ottr:Manufacturing0.00.0

us-gaap:OperatingSegments, ottr:Wholesale, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value4.5071.7161.50.7650.8760.9081.6310.9411.5271.3552.8262.5391.0151.5731.5491.184
Percentage of Revenues1.70.80.60.40.40.40.70.40.60.61.21.10.40.80.70.6
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.00.60.40.40.40.70.40.60.61.21.10.40.80.70.6
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Wholesale ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, us-gaap:ElectricTransmission, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value1111129.673106.51911111011121111
Percentage of Revenues4.64.95.25.04.63.05.15.04.45.05.55.04.9
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.05.25.04.63.05.15.04.45.05.55.04.9
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments us-gaap:ElectricTransmission ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value12311911010310211310297
Percentage of Revenues47.351.153.447.848.257.852.148.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.051.153.447.848.20.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Electric0.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Manufacturing


Revenuesus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value7564594568606573776467686857545958505258595452515655555355494946
Percentage of Revenues29.028.425.423.829.227.928.732.131.629.229.430.128.527.925.128.027.325.926.528.729.028.926.227.328.067.522.922.725.821.523.416.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.025.423.829.227.928.732.131.629.229.430.128.527.925.128.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Plastics


Revenuesus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value6249604846414853403855544938585037324247333247453231514840464442
Percentage of Revenues23.821.825.725.319.819.121.223.316.317.424.224.120.618.727.123.817.416.321.423.216.217.123.524.416.038.921.320.518.820.321.115.2
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.025.725.319.819.121.223.316.317.424.224.120.618.727.123.80.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Plastics0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:Revenues us-gaap:ProductOrService

ottr:Electric


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value123119
Percentage of Revenues47.351.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.051.1
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:Electric0.00.0

ottr:ProductSales


Revenuesus-gaap:
Period End2021-03-312020-03-31
Value138114
Percentage of Revenues52.748.9
Percentage of RegulatedAndUnregulatedOperatingRevenue0.048.9
Percentage of RegulatedAndUnregulatedOperatingRevenue ottr:ProductSales0.00.0

Assets

us-gaap:Assets

us-gaap:Assets


Assets
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-31
Value261825782534238923062273218021142104205220272011200419661944193019121868186118331818185618111815179117141682159616581581160215691634167917001711170817701754
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidatedEntities

srt:ParentCompany


Assetsus-gaap:
Period End2020-12-312019-12-312018-12-312017-12-31
Value12131011926885
Percentage of Assets47.144.545.144.2
Percentage of Assets47.144.545.144.2
Percentage of Assets srt:ParentCompany100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidationItems

us-gaap:CorporateNonSegment


Assetsus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302019-12-312018-12-312017-12-312017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-31
Value555449475444593938393739384279766851555459111112
Percentage of Assets2.12.11.92.02.42.23.02.02.02.02.02.12.12.34.34.23.82.93.23.23.86.77.0
Percentage of Assets2.12.11.92.02.42.23.02.02.02.02.02.12.12.34.34.23.82.93.23.23.86.77.0
Percentage of Assets us-gaap:CorporateNonSegment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Assetsus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302016-12-312015-12-31
Value22422233219120541955193118291752173717281695168716901660163916221520
Percentage of Assets85.686.686.586.084.885.083.982.982.584.283.683.984.384.484.384.883.6
Percentage of Assets85.686.686.586.084.885.083.982.982.584.283.683.984.384.484.384.883.6
Percentage of Assets us-gaap:OperatingSegments ottr:Electric100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, ottr:Manufacturing


Assetsus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-31
Value209191189184201195206211217187186181167167170170166168179179173177137139130127125119122114
Percentage of Assets8.07.47.57.78.88.69.510.010.39.19.29.08.38.58.88.88.79.09.79.89.69.67.67.77.37.47.57.57.47.2
Percentage of Assets8.07.47.57.78.88.69.510.010.39.19.29.08.38.58.88.88.79.09.79.89.69.67.67.77.37.47.57.57.47.2
Percentage of Assets us-gaap:OperatingSegments ottr:Manufacturing100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, ottr:Plastics


Assetsus-gaap:
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-31
Value1119910410210292971041049110099879894918486898781899290879095768378
Percentage of Assets4.23.94.14.34.54.04.55.05.04.55.04.94.45.04.94.74.44.64.84.74.54.85.15.04.95.35.64.85.04.9
Percentage of Assets4.23.94.14.34.54.04.55.05.04.55.04.94.45.04.94.74.44.64.84.74.54.85.15.04.95.35.64.85.04.9
Percentage of Assets us-gaap:OperatingSegments ottr:Plastics100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Liabilities And Stockholders Equity

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:LiabilitiesAndStockholdersEquity


Liabilities
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value26182578253423892306227321802114210420522027201120041966194419301912186818611833181818561811181517911714168215961658158116021569163416791700171117081770
Percentage of LiabilitiesAndStockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilitiesAndStockholdersEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Liabilities
Period End2020-12-312019-12-312018-12-312017-12-31
Value12131011926885
Percentage of LiabilitiesAndStockholdersEquity47.144.545.144.2
Percentage of Assets47.144.545.144.2
Percentage of Assets srt:ParentCompany100.0100.0100.0100.0

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value887870852822800781756744740728725714708696692686679670656636613605597589586572563553534529521571631671676
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets33.933.833.634.434.734.434.735.235.235.535.835.50.034.835.235.335.235.035.134.233.533.332.232.632.332.032.932.933.532.032.633.635.738.30.0

us-gaap:StockholdersEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Stockholders
Period End2020-12-312019-12-312018-12-31
Value870781728
Percentage of StockholdersEquity100.0100.0100.0
Percentage of Assets33.834.435.5
Percentage of Assets srt:ParentCompany71.877.378.7

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLoss


Stockholders
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value-8.566-8.716-6.491-4.059-5.677
Percentage of StockholdersEquity-1.0-1.0-0.8-0.6-0.8
Percentage of Assets-0.3-0.3-0.3-0.2-0.3
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLoss0.00.00.00.00.0

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


Stockholders
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value0.1740.2090.054-0.0850.046
Percentage of StockholdersEquity0.00.00.0-0.00.0
Percentage of Assets0.00.00.0-0.00.0
Percentage of Assets us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value-8.392-8.507-5.96-6.035-6.234-6.437-4.496-4.615-4.76-4.144-5.807-5.971-6.133-5.631-3.695-3.8-3.576-3.648-3.758-3.898-4.295-4.422-4.522-4.663-1.66-1.666-1.728-4.183-4.385-3.4321.487-1.315-3.0
Percentage of StockholdersEquity-0.9-1.0-0.7-0.7-0.8-0.8-0.6-0.6-0.6-0.6-0.8-0.8-0.9-0.8-0.5-0.6-0.5-0.6-0.6-0.6-0.7-0.7-0.8-0.8-0.3-0.3-0.3-0.8-0.8-0.60.2-0.2-0.4
Percentage of Assets-0.3-0.3-0.2-0.3-0.3-0.3-0.2-0.2-0.2-0.2-0.3-0.30.0-0.3-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.3-0.1-0.1-0.1-0.3-0.3-0.20.1-0.10.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value416414398390372364346345342344343342341343339337329313298293290287284278267263255255253253251250241
Percentage of StockholdersEquity46.947.646.747.546.646.745.846.446.347.247.348.048.349.349.950.450.149.348.648.548.648.748.548.647.547.547.848.248.544.339.937.335.8
Percentage of Assets15.916.115.716.316.216.015.916.316.316.816.917.00.017.117.617.717.616.916.316.115.615.815.715.515.615.616.015.415.814.914.214.30.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value207207205204201200198198198198198198198197197196196193190189188187187186183183181181180180180179176
Percentage of StockholdersEquity23.423.824.124.825.225.726.326.726.827.227.327.728.028.429.129.429.930.431.031.331.531.931.932.532.733.133.934.234.631.628.526.726.2
Percentage of Assets7.98.08.18.58.88.89.19.49.49.79.89.90.09.910.210.310.510.410.410.410.210.410.310.410.710.911.410.911.310.610.210.20.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value271257254233231222215205203190189179174161155150146139134132128126123119119112113108999792141198243260
Percentage of StockholdersEquity30.629.629.928.429.028.528.527.627.526.126.125.124.623.122.521.921.620.820.520.821.020.820.620.220.419.720.219.718.618.417.724.731.436.238.5
Percentage of Assets10.410.010.09.810.09.89.99.79.79.39.48.90.08.07.97.77.67.37.27.17.06.96.66.66.66.36.66.56.25.95.88.311.213.90.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Assets Current

us-gaap:AssetsCurrent

us-gaap:AssetsCurrent


Assets
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value258234274266256254237263273241241239239228220218208203214209206273262300307297292250310300323299369375399371368435
Percentage of AssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets9.99.110.811.211.111.210.912.513.011.811.911.911.911.611.311.310.910.911.511.411.414.814.516.617.117.417.415.718.719.020.219.122.622.423.521.721.624.6

us-gaap:AssetsCurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Assets
Period End2020-12-312019-12-312018-12-312017-12-31
Value4.0629.7576.69721
Percentage of AssetsCurrent1.73.82.89.0
Percentage of Assets0.20.40.31.1
Percentage of Assets srt:ParentCompany0.31.00.72.4

Cash And Cash Equivalents At Carrying Value

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:CashAndCashEquivalentsAtCarryingValue


Cash
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302016-12-312015-09-302015-03-312014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312011-12-312011-09-302011-06-302011-03-312009-12-312008-12-31
Value1.2121.16344397.884210.9210.9820.8910.8610.6491.0361.121160.8260.00.5480.1577.3441.1559423752146.6040.01.5845.0416.829
Percentage of CashAndCashEquivalentsAtCarryingValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0
Percentage of Assets0.00.01.81.70.30.90.00.00.00.00.00.10.00.80.00.00.00.00.00.13.60.02.43.30.90.40.00.00.30.0

Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents


Cash
Period End2021-03-312020-12-312020-03-312019-12-312018-12-312017-12-31
Value1.2121.1637.884210.86116
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.30.90.00.8

Accounts Receivable Net Current

us-gaap:AccountsReceivableNetCurrent

us-gaap:AccountsReceivableNetCurrent


Accounts
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1008496779210511375969168877982686978736276677460105101839810291133134139116152148124
Percentage of AccountsReceivableNetCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets4.03.54.23.44.25.05.43.74.74.63.44.44.14.33.63.74.24.03.54.13.74.13.46.16.05.25.96.55.78.58.28.36.98.98.77.0

Inventory Net

us-gaap:InventoryNet

us-gaap:InventoryNet


Inventory
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value9292818998979710510610694908878878183808185858381848578827272736973778277918679
Percentage of InventoryNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets3.53.63.23.84.34.34.55.05.15.24.74.54.44.04.54.24.44.34.44.74.74.54.54.74.84.64.94.64.44.64.34.74.74.94.65.35.04.5

Inventory Raw Materials And Supplies

us-gaap:InventoryRawMaterialsAndSupplies

us-gaap:InventoryRawMaterialsAndSupplies


Inventory
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value5253484952494853504846464745484444454646464747474644464242423841414544504442
Percentage of InventoryRawMaterialsAndSupplies100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets2.02.11.92.12.32.22.22.52.42.42.32.32.42.32.52.32.32.42.52.62.62.62.62.62.62.62.82.62.62.72.42.72.52.72.63.02.62.4

Other Assets Current

us-gaap:OtherAssetsCurrent

us-gaap:OtherAssetsCurrent


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value9.5165.6457.5528.0317.3475.0426.9268.5119.9866.1148.6119.574121614118.14411148.7468.4539.3118.5886.9357.18710137.74710148.16117162021232120
Percentage of OtherAssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.40.20.30.30.30.20.30.40.50.30.40.50.60.80.70.60.40.60.80.50.50.50.50.40.40.60.80.50.60.90.51.11.01.21.31.41.21.1

us-gaap:OtherAssetsCurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Other
Period End2020-12-312019-12-312018-12-312017-12-31
Value1.0631.053.4821.13
Percentage of OtherAssetsCurrent18.820.857.09.0
Percentage of Assets0.00.00.20.1
Percentage of Assets srt:ParentCompany0.10.10.40.1

Assets Noncurrent

us-gaap:AssetsNoncurrent

us-gaap:AssetsNoncurrent


Assets
Period End2021-03-312020-12-312019-12-31
Value235923432018
Percentage of AssetsNoncurrent100.0100.0100.0
Percentage of Assets90.190.988.8

Property Plant And Equipment Gross

us-gaap:PropertyPlantAndEquipmentGross

us-gaap:PropertyPlantAndEquipmentGross


Property
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value293227852697264525702477244024292409238523392306227422482225220221692130210120702032200819681954191318431792170616871700168017511737177817581715
Percentage of PropertyPlantAndEquipmentGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets115.7116.6117.0116.4117.9117.1116.0118.4118.8118.6116.7117.3117.0116.5116.4117.8116.5116.2115.6111.5112.2110.7109.9114.0113.7115.5108.1107.9105.3108.3102.8104.3102.2103.9103.096.9

us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType, us-gaap:PublicUtility

ottr:BuildingsAndLeaseholdImprovements, ottr:NonelectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value5553535251418881
Percentage of PropertyPlantAndEquipmentGross0.02.02.22.22.32.05.14.8
Percentage of Assets2.22.32.62.62.72.35.24.6
Percentage of Assets ottr:BuildingsAndLeaseholdImprovements ottr:NonelectricPlant0.00.00.00.00.00.00.00.0

ottr:DistributionPlant, ottr:ElectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value545526502482466
Percentage of PropertyPlantAndEquipmentGross0.019.920.720.621.0
Percentage of Assets21.123.124.524.124.4
Percentage of Assets ottr:DistributionPlant ottr:ElectricPlant0.00.00.00.00.0

ottr:ElectricPlantInService, ottr:ElectricPlant


Property
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value268225312212201919811860182013721332
Percentage of PropertyPlantAndEquipmentGross0.00.083.683.184.783.686.679.077.7
Percentage of Assets102.598.297.398.498.897.3100.180.775.3
Percentage of Assets ottr:ElectricPlantInService ottr:ElectricPlant0.00.00.00.00.00.00.00.00.0

ottr:GeneralPlant, ottr:ElectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value1231239910092978381
Percentage of PropertyPlantAndEquipmentGross0.04.74.14.34.14.74.84.7
Percentage of Assets4.85.44.85.04.85.44.94.6
Percentage of Assets ottr:GeneralPlant ottr:ElectricPlant0.00.00.00.00.00.00.00.0

ottr:NonelectricOperationsPlant, ottr:NonelectricPlant


Property
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value259258247228216211201310288
Percentage of PropertyPlantAndEquipmentGross0.00.09.49.49.39.59.617.916.8
Percentage of Assets9.910.010.911.110.811.111.118.216.3
Percentage of Assets ottr:NonelectricOperationsPlant ottr:NonelectricPlant0.00.00.00.00.00.00.00.00.0

ottr:TransmissionPlant, ottr:ElectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value690647512500410
Percentage of PropertyPlantAndEquipmentGross0.024.521.121.418.5
Percentage of Assets26.828.525.025.021.5
Percentage of Assets ottr:TransmissionPlant ottr:ElectricPlant0.00.00.00.00.0

us-gaap:ConstructionInProgress, ottr:ElectricPlant


Property
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value77203177170132149644927
Percentage of PropertyPlantAndEquipmentGross0.00.06.77.05.76.73.12.81.6
Percentage of Assets3.07.97.88.36.67.83.52.91.6
Percentage of Assets us-gaap:ConstructionInProgress ottr:ElectricPlant0.00.00.00.00.00.00.00.00.0

us-gaap:ConstructionInProgress, ottr:NonelectricPlant


Property
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value129.297.654118.5113.264155.31614
Percentage of PropertyPlantAndEquipmentGross0.00.00.30.50.40.10.70.30.8
Percentage of Assets0.50.40.30.60.40.20.90.30.8
Percentage of Assets us-gaap:ConstructionInProgress ottr:NonelectricPlant0.00.00.00.00.00.00.00.00.0

us-gaap:ElectricGenerationEquipment, ottr:ElectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value1172915905897891879669660
Percentage of PropertyPlantAndEquipmentGross0.034.637.338.440.141.838.638.5
Percentage of Assets45.540.344.144.846.648.339.437.3
Percentage of Assets us-gaap:ElectricGenerationEquipment ottr:ElectricPlant0.00.00.00.00.00.00.00.0

us-gaap:Equipment, ottr:NonelectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value197187170160155155208190
Percentage of PropertyPlantAndEquipmentGross0.07.17.06.97.07.412.011.1
Percentage of Assets7.78.38.38.08.18.612.310.8
Percentage of Assets us-gaap:Equipment ottr:NonelectricPlant0.00.00.00.00.00.00.00.0

us-gaap:Land, ottr:NonelectricPlant


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value5.96.044.4754.3944.6944.4791316
Percentage of PropertyPlantAndEquipmentGross0.00.20.20.20.20.20.80.9
Percentage of Assets0.20.30.20.20.20.20.80.9
Percentage of Assets us-gaap:Land ottr:NonelectricPlant0.00.00.00.00.00.00.00.0

us-gaap:PropertyPlantAndEquipmentGross us-gaap:PublicUtility

ottr:ElectricPlant


Property
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value276027342390218921132010188414211360
Percentage of PropertyPlantAndEquipmentGross0.00.090.490.190.490.389.781.879.3
Percentage of Assets105.4106.1105.1106.7105.5105.1103.683.676.9
Percentage of Assets ottr:ElectricPlant0.00.00.00.00.00.00.00.00.0

ottr:NonelectricPlant


Property
Period End2021-03-312020-12-312019-12-312016-12-312015-12-312011-12-312010-12-31
Value272268255215216315302
Percentage of PropertyPlantAndEquipmentGross0.00.09.69.710.318.217.6
Percentage of Assets10.410.411.211.211.918.617.1
Percentage of Assets ottr:NonelectricPlant0.00.00.00.00.00.00.0

Construction In Progress Gross

us-gaap:ConstructionInProgressGross

us-gaap:ConstructionInProgressGross


Construction
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value45432123418514173491811831681411381881661531431169879284269269248234210187159887771826354675642
Percentage of ConstructionInProgressGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets17.913.510.18.16.53.52.38.89.08.47.07.19.78.68.07.76.35.44.415.314.914.913.913.712.511.79.65.64.94.55.03.83.23.93.32.4

Accumulated Depreciation Depletion And Amortization Property Plant And Equipment

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment


Accumulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value939923908891877875861848844832799785773761748749740728713708699709700705695676670648637642630670659681666637
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets37.138.739.439.240.341.440.941.341.641.439.939.939.839.439.140.139.839.839.338.238.639.139.141.141.342.440.441.039.840.938.639.938.839.839.036.0

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:PublicUtility

ottr:ElectricPlant


Accumulated
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value796778731699662622592499476
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment0.00.082.082.582.983.282.975.774.7
Percentage of Assets30.430.232.234.133.132.632.629.426.9
Percentage of Assets ottr:ElectricPlant0.00.00.00.00.00.00.00.00.0

ottr:NonelectricPlant


Accumulated
Period End2021-03-312020-12-312019-12-312016-12-312015-12-312011-12-312010-12-31
Value175174160125121160138
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment0.00.018.016.817.124.321.7
Percentage of Assets6.76.87.16.66.79.47.8
Percentage of Assets ottr:NonelectricPlant0.00.00.00.00.00.00.0

Amortization Of Intangible Assets

us-gaap:AmortizationOfIntangibleAssets

us-gaap:AmortizationOfIntangibleAssets


Amortization
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value275000.0284000.0291000.0296000.0298000.0296000.0296000.0296000.0296000.0329000.0345000.0345000.0346000.0336000.0333000.0332000.0333000.0348000.0398000.0357000.0357000.0282000.0244000.0244000.0244000.0245000.0244000.0244000.0245000.0244000.0244000.0244000.0246000.0247000.0215000.0218000.0
Percentage of AmortizationOfIntangibleAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Property Plant And Equipment Net

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:PropertyPlantAndEquipmentNet


Property
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value20602049199218611789175316921602157915811565155215391520150014871477145214281402138713611333129812681248121811671122105710491057105010811077109710921077
Percentage of PropertyPlantAndEquipmentNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets78.779.578.677.977.677.177.675.875.077.077.277.276.877.377.277.077.277.776.776.576.373.373.671.670.872.872.473.167.766.965.567.464.364.463.464.163.960.8

us-gaap:PropertyPlantAndEquipmentNet us-gaap:PublicUtility

ottr:ElectricPlant


Property
Period End2021-03-312020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value1964195516591490145113871292922884
Percentage of PropertyPlantAndEquipmentNet95.395.494.694.294.393.993.285.682.1
Percentage of Assets75.075.873.072.672.472.671.154.250.0
Percentage of Assets ottr:ElectricPlant0.00.00.00.00.00.00.00.00.0

ottr:NonelectricPlant


Property
Period End2021-03-312020-12-312019-12-312016-12-312015-12-312011-12-312010-12-31
Value9693948994155164
Percentage of PropertyPlantAndEquipmentNet4.74.65.46.16.814.415.3
Percentage of Assets3.73.64.24.75.29.19.3
Percentage of Assets ottr:NonelectricPlant0.00.00.00.00.00.00.0

Long Term Investments

us-gaap:LongTermInvestments

us-gaap:LongTermInvestments


Long
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value545110109.4629.8949.7439.6839.228.9619.1238.6498.6298.5998.1568.1258.4178.0658.4138.4118.2847.87510108.5828.7068.8759.3629.3259.4179.4719.929.056111111129.708
Percentage of LongTermInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets2.12.00.40.40.40.40.40.50.40.40.40.40.40.40.40.40.40.40.50.50.50.40.60.60.50.50.50.60.60.60.60.60.60.70.70.70.80.5

us-gaap:LongTermInvestments us-gaap:ConsolidatedEntities

srt:ParentCompany


Long
Period End2020-12-312019-12-312018-12-312017-12-31
Value1061860787724
Percentage of LongTermInvestments2046.18698.78792.28397.4
Percentage of Assets41.237.938.436.2
Percentage of Assets srt:ParentCompany87.485.185.081.9

Goodwill

us-gaap:Goodwill

us-gaap:Goodwill


Goodwill
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value3737373737373737373737373737373737373739393831313138383838383839393939696969
Percentage of Goodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.41.51.51.61.61.71.71.81.81.81.91.91.91.91.91.92.02.02.02.22.22.11.71.71.82.32.32.42.42.52.42.52.42.32.34.14.13.9

us-gaap:Goodwill us-gaap:StatementBusinessSegments

ottr:Manufacturing


Goodwillus-gaap:
Period End2020-12-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value18181818181818181818181818181820201912121212121212121212121212121212
Percentage of Goodwill48.648.648.648.648.648.648.648.648.648.648.648.648.648.648.651.451.449.838.738.738.731.431.431.331.331.331.331.231.230.930.917.517.517.5
Percentage of Assets0.70.80.80.90.90.90.90.90.90.90.90.91.01.01.01.11.11.00.70.70.70.70.70.80.70.80.80.80.70.70.70.70.70.7
Percentage of Assets ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.010.210.68.17.87.47.98.07.88.4

Intangible Assets Net Excluding Goodwill

us-gaap:IntangibleAssetsNetExcludingGoodwill

us-gaap:IntangibleAssetsNetExcludingGoodwill


Intangible
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value9.86910101010111111121212131314141414151515151610111112121313141414141515151516
Percentage of IntangibleAssetsNetExcludingGoodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.40.40.40.40.50.50.50.60.60.60.60.70.70.70.70.80.80.80.80.80.90.90.60.60.60.70.80.80.80.90.90.90.90.90.90.90.90.9

Finite Lived Intangible Assets Net

us-gaap:FiniteLivedIntangibleAssetsNet

us-gaap:FiniteLivedIntangibleAssetsNet


Finite
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value10101010111111121212131314141414151515151610111111111212121313131515131414
Percentage of FiniteLivedIntangibleAssetsNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.40.40.40.50.50.50.60.60.60.60.70.70.70.70.80.80.80.80.80.90.90.60.60.60.70.70.80.80.80.80.90.80.90.90.80.80.8

us-gaap:FiniteLivedIntangibleAssetsNet us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:CustomerRelationships


Finite
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value10101010111111121212121313141414141514141510101111111112121212131313131314
Percentage of FiniteLivedIntangibleAssetsNet99.899.899.799.699.599.699.599.499.399.298.998.197.897.798.197.897.597.196.395.595.097.697.398.097.897.697.196.996.696.496.296.088.988.899.099.099.5
Percentage of Assets0.40.40.40.50.50.50.60.60.60.60.60.70.70.70.70.80.80.80.80.80.80.60.60.60.70.70.70.70.80.80.80.80.80.80.80.80.8
Percentage of Assets us-gaap:CustomerRelationships0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherIntangibleAssets


Finite
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value0.0230.0230.0320.0450.0580.0470.060.0730.0860.0980.1110.1370.1360.0980.0320.0640.0960.1280.160.1920.2240.2560.2870.3520.3830.4470.4790.5110.5431.6751.7070.1280.1330.039
Percentage of FiniteLivedIntangibleAssetsNet0.20.20.30.40.50.40.50.60.70.80.81.01.00.70.20.40.60.81.51.72.02.22.42.93.13.43.63.84.011.111.20.90.90.3
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.10.10.00.00.0
Percentage of Assets us-gaap:OtherIntangibleAssets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Operating Lease Right Of Use Asset

us-gaap:OperatingLeaseRightOfUseAsset

us-gaap:OperatingLeaseRightOfUseAsset


Operating
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value19192021212119200.0
Percentage of OperatingLeaseRightOfUseAsset100.0100.0100.0100.0100.0100.0100.0100.00.0
Percentage of Assets0.70.80.90.91.01.00.91.00.0

Other Assets Noncurrent

us-gaap:OtherAssetsNoncurrent

us-gaap:OtherAssetsNoncurrent


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value2926424038403839383536363634353534333333323130303029302827262626272726272827
Percentage of OtherAssetsNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.11.01.71.71.71.81.81.81.81.71.81.81.81.81.81.81.81.81.81.81.81.71.71.71.71.71.81.81.71.71.61.71.71.71.61.61.71.5

us-gaap:OtherAssetsNoncurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Other
Period End2020-12-312019-12-312018-12-312017-12-31
Value40353131
Percentage of OtherAssetsNoncurrent155.488.388.287.6
Percentage of Assets1.61.61.51.6
Percentage of Assets srt:ParentCompany3.43.53.43.6

Equity Securities Fv Ni

us-gaap:EquitySecuritiesFvNi

us-gaap:EquitySecuritiesFvNi


Equity
Period End2021-03-312020-12-312019-12-31
Value5141000.01662000.01586000.0
Percentage of EquitySecuritiesFvNi100.0100.0100.0
Percentage of Assets0.20.10.1

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring


Equity
Period End2021-03-312020-12-312019-12-31
Value5141000.01662000.01586000.0
Percentage of EquitySecuritiesFvNi100.0100.0100.0
Percentage of Assets0.20.10.1
Percentage of Assets us-gaap:FairValueInputsLevel1 us-gaap:FairValueMeasurementsRecurring0.00.00.0

Accounts Payable Current

us-gaap:AccountsPayableCurrent

us-gaap:AccountsPayableCurrent


Accounts
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value113130189133991208911110096919584969483897786898996101951071071081131098788103118121115113121113
Percentage of AccountsPayableCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets4.35.17.55.64.35.34.15.34.84.74.54.74.24.94.94.34.74.24.64.94.95.25.65.36.06.36.57.16.65.55.56.67.37.26.86.77.16.4

Liabilities Current

us-gaap:LiabilitiesCurrent

us-gaap:LiabilitiesCurrent


Liabilities
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value459436299232175189253206200170163166256246236235215246233232271237198214201199186232219158173176233186187215213276
Percentage of LiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets17.516.911.89.77.68.311.69.79.58.38.18.312.812.512.212.211.313.212.512.714.912.810.911.811.311.711.114.613.210.010.811.214.311.111.012.612.515.6

us-gaap:LiabilitiesCurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Liabilities
Period End2020-12-312019-12-312018-12-312017-12-31
Value2121058069
Percentage of LiabilitiesCurrent48.755.647.027.2
Percentage of Assets8.24.63.93.5
Percentage of Assets srt:ParentCompany17.510.48.67.9

Long Term Debt Current

us-gaap:LongTermDebtCurrent

us-gaap:LongTermDebtCurrent


Long
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1391400.2150.2610.3060.1830.180.1770.1740.1720.1690.1670.1860.197424533855252520.2210.2070.2040.2010.1980.1940.1880.1850.1790.1760.173503.03.0333.2863.340.604
Percentage of LongTermDebtCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.35.40.00.00.00.00.00.00.00.00.00.00.00.02.22.31.74.62.82.92.90.00.00.00.00.00.00.00.00.00.00.03.10.20.20.20.20.0

us-gaap:LongTermDebtCurrent us-gaap:ConsolidatedEntities

ottr:OtterTailPowerCompany


Long
Period End2020-12-312019-09-302019-06-302018-12-312016-12-31
Value1390.00.00.032
Percentage of LongTermDebtCurrent99.90.00.00.099.3
Percentage of Assets5.40.00.00.01.7
Percentage of Assets ottr:OtterTailPowerCompany0.00.00.00.00.0

srt:ParentCompany


Long
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.1690.2150.2610.3060.1830.180.1770.1740.1720.1690.1670.186
Percentage of LongTermDebtCurrent0.1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets srt:ParentCompany0.00.00.00.00.00.00.00.00.00.00.00.0

Operating Lease Liability Current

us-gaap:OperatingLeaseLiabilityCurrent

us-gaap:OperatingLeaseLiabilityCurrent


Operating
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value4479000.04581000.04543000.04197000.04136000.04006000.03784000.03900000.00
Percentage of OperatingLeaseLiabilityCurrent100.0100.0100.0100.0100.0100.0100.0100.00.0
Percentage of Assets0.20.20.20.20.20.20.20.20.0

Other Liabilities Current

us-gaap:OtherLiabilitiesCurrent

us-gaap:OtherLiabilitiesCurrent


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value21228.927108.864107.409118.575129.373121114151515161716157.466128.898.7938.2868.6956.5327.7347.166.3346.9235.547.8425.54118.4649.546
Percentage of OtherLiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.80.90.40.50.40.50.30.50.40.60.50.60.60.70.80.80.80.91.00.90.80.40.70.50.50.50.50.40.50.50.40.40.30.50.30.70.50.5

us-gaap:OtherLiabilitiesCurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Other
Period End2020-12-312019-12-312018-12-312017-12-31
Value129.4739.9947.799
Percentage of OtherLiabilitiesCurrent57.586.882.368.5
Percentage of Assets0.50.40.50.4
Percentage of Assets srt:ParentCompany1.10.91.10.9

Liabilities Noncurrent

us-gaap:LiabilitiesNoncurrent

us-gaap:LiabilitiesNoncurrent


Liabilities
Period End2021-03-312020-12-312019-12-31
Value646646612
Percentage of LiabilitiesNoncurrent100.0100.0100.0
Percentage of Assets24.725.127.0

Long Term Debt

us-gaap:LongTermDebt

us-gaap:LongTermDebt


Long
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value767767767727727692592592592592592592492492534537540548548548498498498498498498498389437437421421472474474436437435
Percentage of LongTermDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets29.329.830.330.431.530.527.228.028.228.929.229.524.625.127.527.928.329.329.529.927.426.927.527.527.829.129.624.426.427.726.326.928.928.327.925.525.624.6

Long Term Debt Noncurrent

us-gaap:LongTermDebtNoncurrent

us-gaap:LongTermDebtNoncurrent


Long
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value624624764724724689590590590590589589490490490490505460493493443498498498498498498389437437421421421471471433433434
Percentage of LongTermDebtNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets23.824.230.230.331.430.327.127.928.028.729.129.324.524.925.225.426.424.726.526.924.426.827.527.527.829.129.624.426.427.726.326.925.828.127.825.325.424.6

us-gaap:LongTermDebtNoncurrent us-gaap:ConsolidatedEntities

ottr:OtterTailPowerCompany


Long
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312016-12-31
Value544684644644609510510510510510509410410
Percentage of LongTermDebtNoncurrent87.289.689.089.088.486.586.586.586.586.486.483.781.2
Percentage of Assets21.127.027.028.026.823.424.124.224.925.225.420.521.4
Percentage of Assets ottr:OtterTailPowerCompany0.00.00.00.00.00.00.00.00.00.00.00.00.0

srt:ParentCompany


Long
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value797979797979797979798080
Percentage of LongTermDebtNoncurrent12.810.411.011.011.613.513.513.513.513.613.616.3
Percentage of Assets3.13.13.33.53.53.73.83.83.93.94.04.0
Percentage of Assets srt:ParentCompany6.60.00.00.07.90.00.00.08.60.00.09.0

Deferred Income Tax Liabilities Net

us-gaap:DeferredIncomeTaxLiabilitiesNet

us-gaap:DeferredIncomeTaxLiabilitiesNet


Deferred
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312018-12-31
Value160153152141137131120
Percentage of DeferredIncomeTaxLiabilitiesNet100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets6.15.96.05.96.05.85.9

Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent

us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap:RetirementPlanType

us-gaap:PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent

us-gaap:PensionPlansDefinedBenefit


Pension
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value6755586760
Percentage of PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent100.0100.0100.0100.0100.0
Percentage of Assets2.62.42.93.43.2
Percentage of Assets us-gaap:PensionPlansDefinedBenefit0.00.00.00.00.0

Other Liabilities Noncurrent

us-gaap:OtherLiabilitiesNoncurrent

us-gaap:OtherLiabilitiesNoncurrent


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value6360353430302828262425252222222221252423232424242621222525232221222619192021
Percentage of OtherLiabilitiesNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets2.42.31.41.51.31.41.31.41.31.21.31.21.11.21.21.11.11.41.31.31.31.31.31.31.51.31.31.61.61.51.41.41.41.61.11.21.21.2

us-gaap:OtherLiabilitiesNoncurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Other
Period End2020-12-312019-12-312018-12-312017-12-31
Value50443738
Percentage of OtherLiabilitiesNoncurrent84.2142.8155.4168.3
Percentage of Assets2.01.91.81.9
Percentage of Assets srt:ParentCompany4.24.44.14.3

Operating Lease Liability Noncurrent

us-gaap:OperatingLeaseLiabilityNoncurrent

us-gaap:OperatingLeaseLiabilityNoncurrent


Operating
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value15151617181816170.0
Percentage of OperatingLeaseLiabilityNoncurrent100.0100.0100.0100.0100.0100.0100.0100.00.0
Percentage of Assets0.60.60.70.80.80.80.80.80.0

Lessee Operating Lease Liability Payments Due Year Two

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value4282000.04945000.04998000.04987000.05063000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearTwo100.0100.0100.0100.0100.0
Percentage of Assets0.20.20.20.20.2

Lessee Operating Lease Liability Payments Due Year Three

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value3905000.03914000.04719000.04700000.04748000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearThree100.0100.0100.0100.0100.0
Percentage of Assets0.20.20.20.20.2

Lessee Operating Lease Liability Payments Due Year Four

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value3376000.03571000.03697000.03672000.03736000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFour100.0100.0100.0100.0100.0
Percentage of Assets0.10.20.20.20.2

Lessee Operating Lease Liability Payments Due Year Five

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value2545000.03087000.03399000.03370000.03405000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFive100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.2

Lessee Operating Lease Liability Payments Due After Year Five

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value3301000.05587000.08427000.08469000.08470000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive100.0100.0100.0100.0100.0
Percentage of Assets0.10.20.40.40.4

Operating Lease Liability

us-gaap:OperatingLeaseLiability

us-gaap:OperatingLeaseLiability


Operating
Period End2020-12-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value192222192120
Percentage of OperatingLeaseLiability100.0100.0100.0100.0100.0100.0
Percentage of Assets0.81.01.00.91.01.0

Lessee Operating Lease Liability Payments Due

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value2226262729
Percentage of LesseeOperatingLeaseLiabilityPaymentsDue100.0100.0100.0100.0100.0
Percentage of Assets0.91.21.21.31.4

Lessee Operating Lease Liability Undiscounted Excess Amount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount


Lessee
Period End2020-12-312019-12-312019-09-302019-06-302019-03-31
Value3003000.03987000.04154000.04429000.04731000.0
Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount100.0100.0100.0100.0100.0
Percentage of Assets0.10.20.20.20.2

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value887870852822800781756744740728725714708696692686679670656636613605597589586572563553534529521571631671676
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets33.933.833.634.434.734.434.735.235.235.535.835.50.034.835.235.335.235.035.134.233.533.332.232.632.332.032.932.933.532.032.633.635.738.30.0

us-gaap:StockholdersEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Stockholders
Period End2020-12-312019-12-312018-12-31
Value870781728
Percentage of StockholdersEquity100.0100.0100.0
Percentage of Assets33.834.435.5
Percentage of Assets srt:ParentCompany71.877.378.7

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLoss


Stockholders
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value-8.566-8.716-6.491-4.059-5.677
Percentage of StockholdersEquity-1.0-1.0-0.8-0.6-0.8
Percentage of Assets-0.3-0.3-0.3-0.2-0.3
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLoss0.00.00.00.00.0

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


Stockholders
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value0.1740.2090.054-0.0850.046
Percentage of StockholdersEquity0.00.00.0-0.00.0
Percentage of Assets0.00.00.0-0.00.0
Percentage of Assets us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value-8.392-8.507-5.96-6.035-6.234-6.437-4.496-4.615-4.76-4.144-5.807-5.971-6.133-5.631-3.695-3.8-3.576-3.648-3.758-3.898-4.295-4.422-4.522-4.663-1.66-1.666-1.728-4.183-4.385-3.4321.487-1.315-3.0
Percentage of StockholdersEquity-0.9-1.0-0.7-0.7-0.8-0.8-0.6-0.6-0.6-0.6-0.8-0.8-0.9-0.8-0.5-0.6-0.5-0.6-0.6-0.6-0.7-0.7-0.8-0.8-0.3-0.3-0.3-0.8-0.8-0.60.2-0.2-0.4
Percentage of Assets-0.3-0.3-0.2-0.3-0.3-0.3-0.2-0.2-0.2-0.2-0.3-0.30.0-0.3-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.3-0.1-0.1-0.1-0.3-0.3-0.20.1-0.10.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value416414398390372364346345342344343342341343339337329313298293290287284278267263255255253253251250241
Percentage of StockholdersEquity46.947.646.747.546.646.745.846.446.347.247.348.048.349.349.950.450.149.348.648.548.648.748.548.647.547.547.848.248.544.339.937.335.8
Percentage of Assets15.916.115.716.316.216.015.916.316.316.816.917.00.017.117.617.717.616.916.316.115.615.815.715.515.615.616.015.415.814.914.214.30.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value207207205204201200198198198198198198198197197196196193190189188187187186183183181181180180180179176
Percentage of StockholdersEquity23.423.824.124.825.225.726.326.726.827.227.327.728.028.429.129.429.930.431.031.331.531.931.932.532.733.133.934.234.631.628.526.726.2
Percentage of Assets7.98.08.18.58.88.89.19.49.49.79.89.90.09.910.210.310.510.410.410.410.210.410.310.410.710.911.410.911.310.610.210.20.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


Stockholders
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302012-12-312011-12-312010-12-312009-12-312008-12-31
Value271257254233231222215205203190189179174161155150146139134132128126123119119112113108999792141198243260
Percentage of StockholdersEquity30.629.629.928.429.028.528.527.627.526.126.125.124.623.122.521.921.620.820.520.821.020.820.620.220.419.720.219.718.618.417.724.731.436.238.5
Percentage of Assets10.410.010.09.810.09.89.99.79.79.39.48.90.08.07.97.77.67.37.27.17.06.96.66.66.66.36.66.56.25.95.88.311.213.90.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue


Common
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value207207205204201200198198198198198198197197197197196196193190189188187187186183183181181181180180180180180180180180
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets7.98.08.18.58.88.89.19.49.49.79.89.99.910.110.210.210.310.510.410.410.410.210.410.310.410.710.911.410.911.411.311.511.110.810.610.510.610.2

Additional Paid In Capital Common Stock

us-gaap:AdditionalPaidInCapitalCommonStock

us-gaap:AdditionalPaidInCapitalCommonStock


Additional
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value416414398390372364346345342344343342343342341339337329313298293290287284278267263255255254253253253253253252251251
Percentage of AdditionalPaidInCapitalCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets15.916.115.716.316.216.015.916.316.316.816.917.017.117.417.617.617.717.616.916.316.115.615.815.715.515.615.616.015.416.115.816.115.515.114.914.714.714.2

Retained Earnings Accumulated Deficit

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:RetainedEarningsAccumulatedDeficit


Retained
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value27125725423323122221520520319018917916115515014613913413212812612311911911211310899979692100109137141196200198
Percentage of RetainedEarningsAccumulatedDeficit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets10.410.010.09.810.09.89.99.79.79.39.48.98.07.97.77.67.37.27.17.06.96.66.66.66.36.66.56.25.96.15.86.46.78.28.311.511.811.2

Accumulated Other Comprehensive Income Loss Net Of Tax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax


Accumulated
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-31
Value-8392000.0-8507000.0-5960000.0-6035000.0-6234000.0-6437000.0-4496000.0-4615000.0-4760000.0-4144000.0-5807000.0-5971000.0-5631000.0-3459000.0-3586000.0-3695000.0-3800000.0-3576000.0-3648000.0-3758000.0-3898000.0-4295000.0-4422000.0-4522000.0-4663000.0-1660000.0-1666000.0-1728000.0-4183000.0-4317000.0-4385000.0-3141000.0-3244000.0-3308000.0-3432000.0-2879000.0-2924000.01487000.0-1315000.0
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-0.3-0.3-0.2-0.3-0.3-0.3-0.2-0.2-0.2-0.2-0.3-0.3-0.3-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.2-0.3-0.1-0.1-0.1-0.3-0.3-0.3-0.2-0.2-0.2-0.2-0.2-0.20.1-0.1

Stock Issued During Period Value New Issues

us-gaap:StockIssuedDuringPeriodValueNewIssues

us-gaap:StockIssuedDuringPeriodValueNewIssues


Stock
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-0.025177.902188.27519-0.0360.0170.00.0-0.0930.00.0832.3222.5644.50717185.493.324.2133.1137.522124.777
Percentage of StockIssuedDuringPeriodValueNewIssues100.0100.0100.0100.0100.0100.0100.0100.00.00.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-03-312018-03-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-0.407146.885166.99-0.601-0.6381.7273.88915154.412.6653.3772.3716.302103.907
Percentage of StockIssuedDuringPeriodValueNewIssues1628.087.787.187.384.50.00.067.486.385.382.680.380.380.276.283.882.981.8
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


Stock
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0.3822.0881.0172.3621.2852.0120.0010.1260.6010.00.1260.1290.6380.8370.6182.6063.1691.080.6550.8360.7421.222.1260.87
Percentage of StockIssuedDuringPeriodValueNewIssues-1528.012.312.912.715.510.2-2.8741.20.00.00.0-138.70.032.613.714.717.419.719.719.823.816.217.118.2
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue


Adjustments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value4197000.01002000.01275000.01237000.02770000.0713000.01301000.02148000.01796000.01039000.01149000.01107000.01146000.0877000.0845000.0770000.01150000.02015000.0335000.0339000.0489000.0288000.0302000.0503000.0623000.0657000.0390000.0
Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Adjustments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value4197000.01002000.01275000.01237000.02770000.0713000.01301000.02148000.01796000.01039000.01149000.01107000.01146000.01150000.02015000.0335000.0339000.0489000.0288000.0302000.0503000.0623000.0657000.0390000.0
Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value1570675221793552174247484.645944482148504122472850-8.35654223-19.05746397.813103377.8512439336.9614411
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.028.627.09.337.015.722.77.019.320.821.51.928.820.722.70.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value-49.02-153.267-101.38-45.946-75.059-58.342-95.747-29.947-25.436-31.485-26.215-25.892-23.827-37.339-38.633-26.609-30.009-35.917-45.11-52.699-25.598-36.498-63.914-37.204-18.354-40.73-44.569-42.03-37.167-57.868-23.276-13.264-28.304-28.417-23.161-4.794-23.03656-23.458-23.34-23.453
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-43.0-23.8-32.0-27.1-41.9-13.1-10.3-14.2-11.5-11.4-9.9-18.1-17.8-12.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value3338392539-1.26859-22.0998.316-10.891-21.637-22.9484.092-6.771-5.346-21.4628.808-12.726-5.471112.961-11.37335-13.44127-24.7271.723126128-11.014-8.601-75.561-9.2491.331-11.842-9.995-90.8917-20.44112
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.016.713.217.0-0.626.2-9.63.4-4.9-9.5-10.11.7-3.3-2.5-10.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect


Cash
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value0.049-43.7415.39231-13.31520-0.061
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.02.316.4-5.79.4-0.0

Deferred Income Tax Expense Benefit

us-gaap:DeferredIncomeTaxExpenseBenefit

us-gaap:DeferredIncomeTaxExpenseBenefit


Deferred
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value5.697-5.152103.665.8128.022.5270.1250.835115.453-0.8252.9018.3217.0144.1544.5124.25.2454.3495.3313-0.4635.6697.0387.385.9741.777135.3333.7436.1396.119-1.915-7.7173.1484.5331.4874.124-8.6039.826
Percentage of DeferredIncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Depreciation Depletion And Amortization

us-gaap:DepreciationDepletionAndAmortization

us-gaap:DepreciationDepletionAndAmortization


Depreciation
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value222020202019191919181818181817171718181818161514141315141415141415171711191917121918
Percentage of DepreciationDepletionAndAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Increase Decrease In Inventories

us-gaap:IncreaseDecreaseInInventories

us-gaap:IncreaseDecreaseInInventories


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value0.26110-7.883-8.3980.3010.799-8.808-0.8720.462114.182.436-0.0359.119-8.3525.794-2.2672.892-0.548-4.212-0.0063.761-2.321-2.712-0.6886.279-3.7590.8219.236-0.7520.0134.062-3.937-5.5914.976-5.8714.8795.2911.6757.473-4.17
Percentage of IncreaseDecreaseInInventories100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value1570675221793552174247484.645944482148504122472850-8.35654223-19.05746397.813103377.8512439336.9614411
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.028.627.09.337.015.722.77.019.320.821.51.928.820.722.70.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value3018351624202415261423182618171619171415141415111710159.99321157.701151.873-17.3567.243-44.1356.368185.6962.0566.101-14.218
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.015.28.810.39.410.86.710.76.410.28.310.98.98.27.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems

us-gaap:CorporateNonSegment


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302017-06-302017-03-312016-06-302016-03-31
Value-1.79-3.117-2.457-1.693-2.29-1.376-1.489-1.858-1.009-0.64-0.086-2.053
Percentage of NetIncomeLoss-5.9-16.7-6.8-10.0-9.4-6.8-6.0-12.0-6.0-3.3-0.5-14.1
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-1.0-0.9-1.0-0.6-0.7-0.8-0.50.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:CorporateNonSegment0.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value171224131615177.502181214101612101015129.148
Percentage of NetIncomeLoss58.067.268.878.466.774.571.548.671.088.962.656.763.670.261.360.489.385.658.4
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.010.56.96.97.07.73.37.65.76.44.76.96.25.04.80.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Electric0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Manufacturing


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value5.3852.5723.3110.2384.9270.9123.1553.994.8422.073.0223.5834.1644.3151.6082.9552.172-0.4141.2463.0091.853
Percentage of NetIncomeLoss17.813.89.21.420.34.512.825.918.414.613.019.215.923.59.117.611.1-2.48.519.212.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.01.40.12.10.41.41.72.00.91.31.61.72.10.71.40.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Manufacturing0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, ottr:Plastics


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value9.1476.66105.135.4495.6545.3975.7923.7294.3146.4326.2296.8448.536.0924.6372.4372.6452.3463.4852.152
Percentage of NetIncomeLoss30.235.728.830.222.527.821.837.514.230.527.633.326.146.534.427.612.415.116.122.214.8
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.04.42.72.32.62.42.51.52.02.82.82.84.12.82.20.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:OperatingSegments ottr:Plastics0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value301835162420241526142318261817161917141514141511171015
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.015.28.810.39.410.86.710.76.410.28.310.98.98.27.90.00.00.00.00.00.00.00.00.00.00.0
Percentage of RegulatedAndUnregulatedOperatingRevenue us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Share Based Compensation

us-gaap:ShareBasedCompensation

us-gaap:ShareBasedCompensation


Share
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value4197000.01002000.01275000.01237000.02770000.0713000.01301000.02148000.01796000.01039000.01149000.01107000.01146000.0877000.0845000.0770000.01150000.02027000.0323000.0339000.0489000.0288000.0302000.0503000.0623000.0657000.0390000.0378000.0358000.0330000.0394000.0392000.0318000.0325000.0287000.0417000.0839000.0469000.0452000.0950000.0653000.0
Percentage of ShareBasedCompensation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value-49.02-153.267-101.38-45.946-75.059-58.342-95.747-29.947-25.436-31.485-26.215-25.892-23.827-37.339-38.633-26.609-30.009-35.917-45.11-52.699-25.598-36.498-63.914-37.204-18.354-40.73-44.569-42.03-37.167-57.868-23.276-13.264-28.304-28.417-23.161-4.794-23.03656-23.458-23.34-23.453
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.0-43.0-23.8-32.0-27.1-41.9-13.1-10.3-14.2-11.5-11.4-9.9-18.1-17.8-12.50.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Payments To Acquire Productive Assets

us-gaap:PaymentsToAcquireProductiveAssets

us-gaap:PaymentsToAcquireProductiveAssets


Payments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value5015010044755795292430252523383826303546542444314735384443375827232733362.342327200.16722
Percentage of PaymentsToAcquireProductiveAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value3338392539-1.26859-22.0998.316-10.891-21.637-22.9484.092-6.771-5.346-21.4628.808-12.726-5.471112.961-11.37335-13.44127-24.7271.723126128-11.014-8.601-75.561-9.2491.331-11.842-9.995-90.8917-20.44112
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RegulatedAndUnregulatedOperatingRevenue0.00.016.713.217.0-0.626.2-9.63.4-4.9-9.5-10.11.7-3.3-2.5-10.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Proceeds From Issuance Of Long Term Debt

us-gaap:ProceedsFromIssuanceOfLongTermDebt

us-gaap:ProceedsFromIssuanceOfLongTermDebt


Proceeds
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312016-12-312016-09-302014-12-312014-09-302013-09-302011-12-312011-09-302010-09-30
Value0.0400.0351000.00.00.00.00.00.0100800.00.00.00.01390.00.0
Percentage of ProceedsFromIssuanceOfLongTermDebt0.0100.00.0100.0100.00.00.00.00.00.00.0100.0100.00.00.00.00.0100.00.00.0

Repayments Of Long Term Debt

us-gaap:RepaymentsOfLongTermDebt

us-gaap:RepaymentsOfLongTermDebt


Repayments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value0.1690.0460.0460.0450.0450.0440.0440.0420.0420.0410.0410.0470.060.059423.0573.057870.0550.0540.0520.0630.050.050.0490.0490.0460.047400.0440.04425502.8790.071000.3150.2980.07-0.2210.473
Percentage of RepaymentsOfLongTermDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Payments Of Dividends

us-gaap:PaymentsOfDividends

us-gaap:PaymentsOfDividends


Payments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value16151514141313131313131313
Percentage of PaymentsOfDividends100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Payments For Repurchase Of Common Stock

us-gaap:PaymentsForRepurchaseOfCommonStock

us-gaap:PaymentsForRepurchaseOfCommonStock


Payments
Period End2021-03-312020-03-312019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302011-12-312011-09-302010-12-312010-09-30
Value1.5072.0720.02.73-0.0010.5620.0412.4090.00.00.041.7590.00.00.0510.0530.00.1750.1821.2390.1310.00.2170.2420.01.030.00.00.0
Percentage of PaymentsForRepurchaseOfCommonStock100.0100.00.0100.0100.0100.0100.0100.00.00.0100.0100.00.00.0100.0100.00.0100.0100.0100.0100.00.0100.0100.00.0100.00.00.00.0

Effective Income Tax Rate Continuing Operations

us-gaap:EffectiveIncomeTaxRateContinuingOperations

us-gaap:EffectiveIncomeTaxRateContinuingOperations


Effective
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value14.8-2.020.20.1830.189-0.0060.1660.1780.176-0.0220.240.140.1260.010.2840.2610.246-0.0160.2610.2460.2750.040.2930.2270.2280.0170.2590.130.2820.2570.2180.279-0.8410.4620.030.2270.2350.0820.1921.084-0.1760.323
Percentage of EffectiveIncomeTaxRateContinuingOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Liabilities

us-gaap:DeferredTaxLiabilities

us-gaap:DeferredTaxLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value153131120100226207354342
Percentage of DeferredTaxLiabilities100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Assets Net

us-gaap:DeferredTaxAssetsNet

us-gaap:DeferredTaxAssetsNet


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value187201200211215229189197
Percentage of DeferredTaxAssetsNet100.0100.0100.0100.0100.0100.0100.0100.0

Unrecognized Tax Benefits

us-gaap:UnrecognizedTaxBenefits

us-gaap:UnrecognizedTaxBenefits


Unrecognized
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302012-12-312012-09-302012-06-302011-12-312010-12-312009-12-312008-12-31
Value0.7710.8591.5271.5291.4881.3021.3151.321.2820.6170.7120.6760.6840.9331.0380.9340.8910.4370.4940.4840.4680.5890.3080.2660.2224.4954.3764.3764.2394.2453.9924.4363.7843.784120.90.90.284
Percentage of UnrecognizedTaxBenefits100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Assets Valuation Allowance

us-gaap:DeferredTaxAssetsValuationAllowance

us-gaap:DeferredTaxAssetsValuationAllowance


Deferred
Period End2020-12-312019-12-312018-12-31
Value800000.0800000.0600000.0
Percentage of DeferredTaxAssetsValuationAllowance100.0100.0100.0

Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions

us-gaap:UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions

us-gaap:UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions


Unrecognized
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value52000.042000.040000.041000.0186000.078000.037000.038000.0665000.041000.036000.036000.0-77000.073000.0104000.043000.088000.0010000.016000.0-121000.045000.042000.044000.0
Percentage of UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0

Proceeds From Repayments Of Short Term Debt

us-gaap:ProceedsFromRepaymentsOfShortTermDebt

us-gaap:ProceedsFromRepaymentsOfShortTermDebt


Proceeds
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value53327.3612113-102.99772-6.999253.11-5.488-9.342-82.0528.73445-1.059165.71-12.1016.338-37.736-6.2843-5.61237-28.1461016-39.29639-0.2181.3351.1437.9633.311-39.0758.713-86.61437-14.48326
Percentage of ProceedsFromRepaymentsOfShortTermDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:AccountsReceivableAllowanceForCreditLossWriteoffAfterRecovery

ottr:AccountsReceivableAllowanceForCreditLossWriteoffAfterRecovery


Accounts
Period End2021-03-312020-03-31
Value443000.0293000.0
Percentage of AccountsReceivableAllowanceForCreditLossWriteoffAfterRecovery100.0100.0

ottr:ChangeInChecksWrittenInExcessOfCash

ottr:ChangeInChecksWrittenInExcessOfCash


Change
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value2144000.0-4759000.0460000.0-550000.003197000.0-1503000.01128000.0-8000.0338000.02243000.0102000.0-2338000.02392000.0-3783000.06956000.0-7999000.02522000.0-1183000.01358000.0666000.0-4093000.0289000.0-289000.01236000.0-1130000.01908000.0
Percentage of ChangeInChecksWrittenInExcessOfCash100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms dei:LegalEntity, us-gaap:LitigationCase

ottr:ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms

ottr:OtterTailPowerCompany, ottr:MISOROEIncentiveSubjectToRecoveryUnderMinnesotaTransmissionCostRecoveryRider


Changes
Period End2020-09-30
Value2600000.0
Percentage of ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms100.0

ottr:ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, us-gaap:Retail, ottr:Electric


Changes
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value2778000.0209000.0-87000.02633000.0-921000.0369000.0-1049000.02318000.0-317000.0-1565000.0-875000.0-779000.0471000.0-424000.0
Percentage of ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms106.80.00.00.00.00.00.00.00.00.00.00.00.00.0

ottr:ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms us-gaap:ProductOrService

us-gaap:Electricity


Changes
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value2778000.0209000.0-87000.02633000.0-921000.0369000.0-1049000.02318000.0-317000.0-1565000.0-875000.0-779000.0471000.0-424000.0
Percentage of ChangesInAccruedRevenuesUnderAlternativeRevenuePrograms106.80.00.00.00.00.00.00.00.00.00.00.00.00.0

ottr:CurrentProjectCapitalizedCost dei:LegalEntity, us-gaap:CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProject

ottr:CurrentProjectCapitalizedCost

ottr:OtterTailPowerCompany, ottr:AstoriaStationProject


Current
Period End2020-09-302020-06-302020-03-31
Value233078
Percentage of CurrentProjectCapitalizedCost100.0100.0100.0

ottr:CurrentProjectCapitalizedCost dei:LegalEntity, us-gaap:CounterpartyName, us-gaap:CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProject

ottr:OtterTailPowerCompany, ottr:EDF, ottr:MerricourtProject


Current
Period End2020-09-302020-06-302020-03-31
Value993595
Percentage of CurrentProjectCapitalizedCost421.2119.7122.8

ottr:CurrentReturnOnEquityUsedInTransmissionRates dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency

ottr:CurrentReturnOnEquityUsedInTransmissionRates

ottr:OtterTailPowerCompany, ottr:ComplaintPeriodBeginningSeptember2016, ottr:FederalEnergyRegulatoryCommission


Current
Period End2020-09-30
Value10.712
Percentage of CurrentReturnOnEquityUsedInTransmissionRates100.0

ottr:OtterTailPowerCompany, ottr:FirstComplaintPeriod, ottr:FederalEnergyRegulatoryCommission


Current
Period End2020-09-302016-09-28
Value10.2170.1082
Percentage of CurrentReturnOnEquityUsedInTransmissionRates95.40.0

ottr:OtterTailPowerCompany, ottr:SecondComplaintPeriod, ottr:FederalEnergyRegulatoryCommission


Current
Period End2020-09-302019-11-212016-09-28
Value12.2560.09880.1238
Percentage of CurrentReturnOnEquityUsedInTransmissionRates114.40.00.0

ottr:DefinedBenefitPlanAmortizationOfGainsLossesFromOtherComprehensiveIncome us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanAmortizationOfGainsLossesFromOtherComprehensiveIncome

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value-124000.0-597000.085000.085000.086000.086000.087000.088000.087000.0226000.0166000.0165000.0165000.0110000.0110000.0110000.0112000.0111000.0111000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLossesFromOtherComprehensiveIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-23000.0-182000.026000.026000.026000.09000.010000.09000.010000.010000.011000.011000.010000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLossesFromOtherComprehensiveIncome18.530.530.630.630.210.511.510.211.54.46.66.76.1

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value-68000.0-385000.055000.055000.055000.035000.026000.026000.027000.046000.046000.047000.044000.031000.031000.032000.032000.032000.032000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLossesFromOtherComprehensiveIncome54.864.564.764.764.040.729.929.531.020.427.728.526.728.228.229.128.628.828.8

ottr:DefinedBenefitPlanAmortizationOfGainsLossesFromRegulatoryAssets us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanAmortizationOfGainsLossesFromRegulatoryAssets

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value-31000.0-164000.024000.024000.023000.031000.031000.031000.031000.0-6000.0-66000.0-67000.067000.0-72000.0-70000.0-72000.0-73000.0-74000.0-73000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLossesFromRegulatoryAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-920000.0-7360000.01051000.0-1052000.0-1051000.0-2749000.0393000.0392000.0393000.0-2884000.0412000.0412000.0412000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLossesFromRegulatoryAssets2967.74487.84379.2-4383.3-4569.6-8867.71267.71264.51267.748066.7-624.2-614.9614.9

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value-2660000.0-15617000.02231000.02231000.02231000.01154000.01163000.01162000.01163000.0-1784000.0-1784000.0-1783000.01784000.0-1272000.0-1273000.0-1272000.0-1288000.0-1411000.0-1227000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLossesFromRegulatoryAssets8580.69522.69295.89295.89700.03722.63751.63748.43751.629733.32703.02661.22662.71766.71818.61766.71764.41906.81680.8

ottr:DefinedBenefitPlanAmortizationOfPriorServiceCostFromOtherComprehensiveIncomeCredit us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanAmortizationOfPriorServiceCostFromOtherComprehensiveIncomeCredit

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value-36000.0-29000.0-28000.0-29000.0-29000.000-32000.011000.011000.0-13000.05000.06000.0
Percentage of DefinedBenefitPlanAmortizationOfPriorServiceCostFromOtherComprehensiveIncomeCredit100.0100.0100.0100.0100.00.00.0100.0100.0100.0100.0100.0100.0

ottr:DefinedBenefitPlanAmortizationOfPriorServiceCostFromRegulatoryAssetsCredit us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanAmortizationOfPriorServiceCostFromRegulatoryAssetsCredit

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value-1397000.0-1169000.0-1169000.0-1170000.0-1169000.000-1236000.0412000.0412000.0-703000.0233000.0233000.0
Percentage of DefinedBenefitPlanAmortizationOfPriorServiceCostFromRegulatoryAssetsCredit100.0100.0100.0100.0100.00.00.0100.0100.0100.0100.0100.0100.0

ottr:EffectiveIncomeTaxRateReconciliationAmortizationOfExcessDeferredTaxes

ottr:EffectiveIncomeTaxRateReconciliationAmortizationOfExcessDeferredTaxes


Effective
Period End2021-03-312020-03-31
Value-2.9-4.1
Percentage of EffectiveIncomeTaxRateReconciliationAmortizationOfExcessDeferredTaxes100.0100.0

ottr:EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsuranceAmount

ottr:EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsuranceAmount


Effective
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value-155000.0-193000.0207000.0-140000.0-50000.0-150000.0-409000.0357000.0-332000.0-17000.0-8000.0-225000.0-118000.0
Percentage of EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsuranceAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsurancePercent

ottr:EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsurancePercent


Effective
Period End2021-03-312020-03-31
Value-0.50.7
Percentage of EffectiveIncomeTaxRateReconciliationCorporateOwnedLifeInsurancePercent100.0100.0

ottr:EffectiveIncomeTaxRateReconciliationDeductionEquityMethodStockAwards

ottr:EffectiveIncomeTaxRateReconciliationDeductionEquityMethodStockAwards


Effective
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value00402000.0-83000.000827000.010000.073000.00624000.054000.00
Percentage of EffectiveIncomeTaxRateReconciliationDeductionEquityMethodStockAwards0.00.0100.0100.00.00.0100.0100.0100.00.0100.0100.00.0

ottr:EffectiveIncomeTaxRateReconciliationTaxCreditProductionPercent

ottr:EffectiveIncomeTaxRateReconciliationTaxCreditProductionPercent


Effective
Period End2021-03-31
Value7.6
Percentage of EffectiveIncomeTaxRateReconciliationTaxCreditProductionPercent100.0

ottr:EquityToTotalCapitalizationRatio dei:LegalEntity

ottr:EquityToTotalCapitalizationRatio

ottr:OtterTailPowerCompany


Equity
Period End2021-03-312017-03-312016-06-302016-03-31
Value52.40.5290.0060.52
Percentage of EquityToTotalCapitalizationRatio100.0100.0100.0100.0

ottr:EquityToTotalCapitalizationRatioBasisForReturnOnEquity dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType

ottr:EquityToTotalCapitalizationRatioBasisForReturnOnEquity

ottr:OtterTailPowerCompany, ottr:The2020GeneralRateCase, ottr:MinnesotaPublicUtilitiesCommission, us-gaap:SubsequentEvent


Equity
Period End2020-11-02
Value52.5
Percentage of EquityToTotalCapitalizationRatioBasisForReturnOnEquity100.0

ottr:IncomeTaxReconciliationAllowanceForFundsUsedDuringConstruction

ottr:IncomeTaxReconciliationAllowanceForFundsUsedDuringConstruction


Income
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-30
Value388000.0248000.0312000.082000.0239000.094000.086000.015000.0138000.0111000.0167000.072000.092000.091000.042000.051000.0150000.037000.057000.0144000.0125000.0100000.044000.0164000.0164000.0133000.0168000.0106000.0
Percentage of IncomeTaxReconciliationAllowanceForFundsUsedDuringConstruction100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:IncomeTaxReconciliationDifferencesReversingInExcessOfFederalRates

ottr:IncomeTaxReconciliationDifferencesReversingInExcessOfFederalRates


Income
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-1678000.0-543000.0-1229000.0-667000.0-933000.0-774000.0-983000.0-500000.0-838000.0-1025000.0-1073000.0
Percentage of IncomeTaxReconciliationDifferencesReversingInExcessOfFederalRates100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalAndStateStatutoryIncomeTaxRate

ottr:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalAndStateStatutoryIncomeTaxRate


Income
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-31
Value115.4057.7767.7174.8798.3087.9645.6557.8029.6758.819107.7058.0497.7938.676.8896.9638.244.473117.7843.7438.2371.596-11.883.9934.6383.2463.879
Percentage of IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalAndStateStatutoryIncomeTaxRate100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:IncreaseDecreaseInDeferredChargesAndOtherAssets

ottr:IncreaseDecreaseInDeferredChargesAndOtherAssets


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value0.543-29.569-2.1260.4785.087-22.6443.2582.421.464-9.70.3324.0146.295-10.048-0.23.075.005-15.6852.915-0.1452.825-2.4322.3697.9323.538-54.664.171.017-0.8882.2982.7194.86.5332.0887.872-36.8984.1961.3826.2661.328-0.44
Percentage of IncreaseDecreaseInDeferredChargesAndOtherAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:IncreaseDecreaseInInterestPayableAndIncomeTaxesReceivablePayableNet

ottr:IncreaseDecreaseInInterestPayableAndIncomeTaxesReceivablePayableNet


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value-2.5252.572-1.8141.958-0.041-2.148-2.5243.862.437-2.536-0.5382.3071.1630.409-2.1850.911-0.3210.801-1.481.6182.4-2.444-1.5951.645-1.5491.55-1.6361.6511.0131.469-1.3891.076-5.714-8.82.251-10.0020.387-0.8681.24511-6.708
Percentage of IncreaseDecreaseInInterestPayableAndIncomeTaxesReceivablePayableNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:IncreaseDecreaseInOtherOperatingLiabilitiesAndIncreaseDecreaseInDeferredLiabilities

ottr:IncreaseDecreaseInOtherOperatingLiabilitiesAndIncreaseDecreaseInDeferredLiabilities


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value1804000.0-31184000.01941000.0-4318000.0-860000.0-23190000.01598000.0-3155000.0-8787000.02223000.0-568000.0-4332000.05091000.0-17469000.0-2483000.02009000.0-1314000.0-8686000.0405000.0-3041000.0-3363000.0-16179000.0-320000.0-3984000.0-41000.0-59778000.0400000.0-1472000.02408000.0-2347000.0-2996000.0-1975000.0-1034000.03204000.0-9299000.0-33425000.0-512000.0-1145000.0-85000.01848000.0-1063000.0
Percentage of IncreaseDecreaseInOtherOperatingLiabilitiesAndIncreaseDecreaseInDeferredLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:PercentageOfTargetAmountAsActualPayment us-gaap:Range, us-gaap:TitleOfIndividual, us-gaap:AwardType, us-gaap:PlanName

ottr:PercentageOfTargetAmountAsActualPayment

srt:Maximum, srt:ExecutiveOfficer, ottr:StockPerformanceAwards, ottr:The2014StockIncentivePlan


Percentage
Period End2020-09-302020-06-302020-03-312019-02-132018-02-05
Value148.501.51.51.5
Percentage of PercentageOfTargetAmountAsActualPayment100.00.0100.0100.0100.0

ottr:RateRiderRatePercentageOfBase dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:TypeOfArrangement

ottr:RateRiderRatePercentageOfBase

ottr:OtterTailPowerCompany, ottr:EnvironmentalCostRecoveryRider, ottr:NorthDakota1, ottr:The2018AnnualUpdate


Rate
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value-0.30690-0.003100
Percentage of RateRiderRatePercentageOfBase100.00.0100.00.00.0

ottr:OtterTailPowerCompany, ottr:EnvironmentalCostRecoveryRider, ottr:NorthDakota1, ottr:The2018RateResetForEffectOfTCJA


Rate
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value5.537100.0559300
Percentage of RateRiderRatePercentageOfBase-1804.20.0-1804.20.00.0

ottr:OtterTailPowerCompany, ottr:GenerationCostRecovery, ottr:NorthDakota1, ottr:The2019InitialRequest


Rate
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value2.521500.0254700
Percentage of RateRiderRatePercentageOfBase-821.60.0-821.60.00.0

ottr:OtterTailPowerCompany, ottr:GenerationCostRecovery, ottr:NorthDakota1, ottr:The2020AnnualUpdate


Rate
Period End2020-09-302020-06-302020-03-31
Value5.980600.06041
Percentage of RateRiderRatePercentageOfBase-1948.70.0-1948.7

ottr:OtterTailPowerCompany, ottr:PhaseInRatePlan, ottr:SouthDakota1, ottr:The2019InitialRequest


Rate
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value3.311500.033450-0.00597
Percentage of RateRiderRatePercentageOfBase-1079.00.0-1079.00.00.0

ottr:OtterTailPowerCompany, ottr:PhaseInRatePlanRecovery, ottr:SouthDakota1, ottr:The2020AnnualUpdate


Rate
Period End2020-09-30
Value6.4435
Percentage of RateRiderRatePercentageOfBase-2099.5

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1, ottr:The2018RateResetForEffectOfTCJA


Rate
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value7.418100.0749300
Percentage of RateRiderRatePercentageOfBase-2417.10.0-2417.10.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1, ottr:The2019AnnualUpdate


Rate
Period End2020-09-302020-06-302020-03-312019-12-312019-09-30
Value-0.221760-0.0022400
Percentage of RateRiderRatePercentageOfBase72.30.072.30.00.0

ottr:OtterTailPowerCompany, ottr:RenewableResourceAdjustment, ottr:NorthDakota1, ottr:The2020AnnualUpdate


Rate
Period End2020-09-302020-06-302020-03-31
Value5.580600.05637
Percentage of RateRiderRatePercentageOfBase-1818.40.0-1818.4

ottr:ReductionInDepreciableLivesIncreaseInDepreciationExpense dei:LegalEntity, us-gaap:RegulatoryAgency

ottr:ReductionInDepreciableLivesIncreaseInDepreciationExpense

ottr:OtterTailPowerCompany, ottr:HootLakeAndSevenHydroelectricPlants


Reduction
Period End2020-07-30
Value1400000.0
Percentage of ReductionInDepreciableLivesIncreaseInDepreciationExpense100.0

us-gaap:AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease

us-gaap:AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease


Allowance
Period End2021-03-312020-03-31
Value211000.0635000.0
Percentage of AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivableWriteOffs

us-gaap:AllowanceForDoubtfulAccountsReceivableWriteOffs


Allowance
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value313000.0317000.0293000.0225000.058000.0121000.0
Percentage of AllowanceForDoubtfulAccountsReceivableWriteOffs100.0100.0100.0100.0100.0100.0

us-gaap:ConcentrationRiskPercentage1 us-gaap:StatementGeographical, us-gaap:ConcentrationRiskByBenchmark, us-gaap:ConcentrationRiskByType

us-gaap:ConcentrationRiskPercentage1

country:US, us-gaap:SalesRevenueNet, us-gaap:GeographicConcentrationRisk


Concentration
Period End2020-09-302020-06-302019-09-302019-06-30
Value98.90.98998.50.985
Percentage of ConcentrationRiskPercentage1100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanContributionsByEmployer us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanContributionsByEmployer

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-01-312020-01-312019-09-302019-01-31
Value10.0111210.0
Percentage of DefinedBenefitPlanContributionsByEmployer100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanContributionsByEmployer us-gaap:RetirementPlanType, us-gaap:SubsequentEventType

us-gaap:PensionPlansDefinedBenefit, us-gaap:SubsequentEvent


Defined
Period End2021-01-312020-01-312019-02-222018-02-19
Value10.01110.020
Percentage of DefinedBenefitPlanContributionsByEmployer100.0100.00.00.0

us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value5.595.5055.5065.5055.5055.3245.3245.3245.3255.35.35.2995.34.8084.8074.8074.8644.8574.866
Percentage of DefinedBenefitPlanExpectedReturnOnPlanAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanInterestCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanInterestCost

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value0.3070.3630.3620.3620.3620.4340.4330.4340.4340.3920.3990.3990.3990.4220.4210.4210.4160.4170.417
Percentage of DefinedBenefitPlanInterestCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value0.4730.5980.5980.5990.5980.7710.770.7720.770.6460.6460.6460.6450.6780.6780.678
Percentage of DefinedBenefitPlanInterestCost154.1164.7165.2165.5165.2177.6177.8177.9177.4164.8161.9161.9161.7160.7161.0161.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value2.9153.2633.2643.2633.2633.6033.6033.6033.6033.3633.3633.3633.3633.5353.5343.5363.5493.6033.521
Percentage of DefinedBenefitPlanInterestCost949.5898.9901.7901.4901.4830.2832.1830.2830.2857.9842.9842.9842.9837.7839.4839.9853.1864.0844.4

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost us-gaap:NatureOfExpense, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost

ottr:CostsIncludedInElectricOperationAndMaintenanceExpenses, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value319000.0306000.0331000.0333000.0242000.0235000.0235000.0223000.0283000.0264000.0283000.0294000.0279000.0278000.0279000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:CostsIncludedInElectricOperationAndMaintenanceExpenses, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1145000.01099000.01185000.01192000.01033000.01007000.01004000.0950000.01195000.01119000.01195000.01247000.01100000.01100000.01100000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost358.9359.2358.0358.0426.9428.5427.2426.0422.3423.9422.3424.1394.3395.7394.3

ottr:CostsIncludedInOTPCapitalExpenditures, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value132000.0144000.0120000.0118000.072000.078000.079000.091000.089000.0108000.089000.078000.0-465000.0247000.0248000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost41.447.136.335.429.833.233.640.831.440.931.426.5-166.788.888.9

ottr:CostsIncludedInOTPCapitalExpenditures, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value471000.0516000.0432000.0423000.0306000.0333000.0336000.0390000.0380000.0455000.0379000.0328000.0238000.0285000.0286000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost147.6168.6130.5127.0126.4141.7143.0174.9134.3172.3133.9111.685.3102.5102.5

ottr:CostsIncludedInOtherNonelectricExpenses, ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value45000.045000.044000.045000.079000.078000.078000.079000.083000.076000.075000.075000.049000.049000.049000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost14.114.713.313.532.633.233.235.429.328.826.525.517.617.617.6

ottr:CostsIncludedInOtherNonelectricExpenses, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value11000.011000.011000.011000.08000.08000.08000.07000.09000.010000.09000.010000.08000.09000.08000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost3.43.63.33.33.33.43.43.13.23.83.23.42.93.22.9

ottr:CostsIncludedInOtherNonelectricExpenses, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value40000.040000.039000.040000.033000.033000.033000.033000.040000.041000.040000.040000.034000.033000.034000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost12.513.111.812.013.614.014.014.814.115.514.113.612.211.912.2

ottr:NonserviceCostsCapitalizedAsRegulatoryAssets, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value136000.0150000.0124000.0122000.0262000.0284000.0288000.0333000.0251000.0301000.0251000.0217000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost42.649.037.536.6108.3120.9122.6149.388.7114.088.773.8

ottr:NonserviceCostsCapitalizedAsRegulatoryAssets, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value12000.013000.012000.011000.0-118000.0-128000.0-130000.0-150000.0-25000.0-29000.0-24000.0-21000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost3.84.23.63.3-48.8-54.5-55.3-67.3-8.8-11.0-8.5-7.1

ottr:NonserviceCostsIncludedInNonserviceCostComponentsOfPostretirementBenefits, ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value470000.0471000.0471000.0471000.0557000.0557000.0558000.0557000.0637000.0645000.0644000.0645000.0617000.0615000.0617000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost147.3153.9142.3141.4230.2237.0237.4249.8225.1244.3227.6219.4221.1221.2221.1

ottr:NonserviceCostsIncludedInNonserviceCostComponentsOfPostretirementBenefits, us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value342000.0328000.0354000.0355000.0911000.0889000.0885000.0840000.0817000.0768000.0818000.0850000.0739000.0739000.0738000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost107.2107.2106.9106.6376.4378.3376.6376.7288.7290.9289.0289.1264.9265.8264.5

ottr:NonserviceCostsIncludedInNonserviceCostComponentsOfPostretirementBenefits, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value31000.031000.032000.033000.0-410000.0-401000.0-399000.0-379000.0-79000.0-74000.0-77000.0-84000.049000.051000.050000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost9.710.19.79.9-169.4-170.6-169.8-170.0-27.9-28.0-27.2-28.617.618.317.9

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost us-gaap:RetirementPlanType

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value509000.0515000.0516000.0515000.0516000.0662000.0661000.0662000.0662000.0745000.0745000.0744000.0745000.0689000.0688000.0689000.0678000.0678000.0678000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost0.0161.4168.6155.6155.0273.6281.3281.7296.9263.3282.2262.9253.4247.0247.5247.00.00.00.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value413000.0940000.0939000.0940000.0939000.01495000.01494000.01495000.01494000.01449000.01451000.01450000.01449000.01273000.01273000.01273000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost0.0294.7306.9284.0282.0617.8635.7636.2670.0512.0549.6512.4492.9456.3457.9456.3

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value1919000.01699000.01699000.01700000.01699000.0844000.0844000.0844000.0844000.01511000.01512000.01513000.01510000.01469000.01469000.01470000.01433000.01614000.01343000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost0.0532.6555.2513.6510.2348.8359.1359.1378.5533.9572.7534.6513.6526.5528.4526.90.00.00.0

us-gaap:DefinedBenefitPlanServiceCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanServiceCost

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value47000.045000.045000.044000.045000.0105000.0104000.0104000.0105000.0108000.0100000.0100000.0100000.072000.073000.072000.063000.063000.063000.0
Percentage of DefinedBenefitPlanServiceCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value430000.0462000.0461000.0462000.0462000.0322000.0321000.0322000.0321000.0381000.0382000.0381000.0382000.0356000.0357000.0356000.0
Percentage of DefinedBenefitPlanServiceCost914.91026.71024.41050.01026.7306.7308.7309.6305.7352.8382.0381.0382.0494.4489.0494.4

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-302016-06-30
Value1866000.01655000.01655000.01656000.01655000.01372000.01373000.01373000.01373000.01614000.01615000.01615000.01615000.01408000.01407000.01407000.01379000.01376000.01381000.0
Percentage of DefinedBenefitPlanServiceCost3970.23677.83677.83763.63677.81306.71320.21320.21307.61494.41615.01615.01615.01955.61927.41954.22188.92184.12192.1

us-gaap:DividendsCommonStockCash

us-gaap:DividendsCommonStockCash


Dividends
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value161515141413131313131313131212121212121111111111111111
Percentage of DividendsCommonStockCash100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DividendsCommonStockCash us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Dividends
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value161515141413131313131313131212121212121111111111111111
Percentage of DividendsCommonStockCash100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsEmployeeStockOwnershipPlanDividends

us-gaap:EffectiveIncomeTaxRateReconciliationDeductionsEmployeeStockOwnershipPlanDividends


Effective
Period End2021-03-312020-03-31
Value0.11.3
Percentage of EffectiveIncomeTaxRateReconciliationDeductionsEmployeeStockOwnershipPlanDividends100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationOtherAdjustments

us-gaap:EffectiveIncomeTaxRateReconciliationOtherAdjustments


Effective
Period End2021-03-312020-03-31
Value0.3-0.5
Percentage of EffectiveIncomeTaxRateReconciliationOtherAdjustments100.0100.0

us-gaap:EffectiveIncomeTaxRateReconciliationTaxCreditsOther

us-gaap:EffectiveIncomeTaxRateReconciliationTaxCreditsOther


Effective
Period End2021-03-312020-03-31
Value0.40.9
Percentage of EffectiveIncomeTaxRateReconciliationTaxCreditsOther100.0100.0

us-gaap:IncomeTaxCreditsAndAdjustments

us-gaap:IncomeTaxCreditsAndAdjustments


Income
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value-186000.0-235000.0-329000.0-328000.0-329000.0-337000.0-337000.0-337000.0-337000.0-351000.0-351000.0-349000.0-354000.0-368000.0-368000.0-368000.0-366000.0-415000.0-414000.0-414000.0-414000.0-470000.0-469000.0-469000.0-470000.0-543000.0-454000.0-453000.0-454000.0-467000.0-472000.0-483000.0-523000.0-523000.0-522000.0-552000.0-553000.0-622000.0-659000.0-678000.0-679000.0
Percentage of IncomeTaxCreditsAndAdjustments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationOtherReconcilingItems

us-gaap:IncomeTaxReconciliationOtherReconcilingItems


Income
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-31
Value-40000.0-22000.0-90000.0-1000.0-73000.071000.042000.024000.0-47000.0-270000.011000.022000.0-231000.0-30000.0-40000.0-148000.0-210000.090000.091000.0-82000.0-15000.0-340000.0477000.0-43000.0-234000.0-55000.0-52000.0-253000.0-386000.0-57000.0
Percentage of IncomeTaxReconciliationOtherReconcilingItems100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationPriorYearIncomeTaxes

us-gaap:IncomeTaxReconciliationPriorYearIncomeTaxes


Income
Period End2020-09-302019-09-302018-09-30
Value172000.0-688000.02109000.0
Percentage of IncomeTaxReconciliationPriorYearIncomeTaxes100.0100.0100.0

us-gaap:IncomeTaxReconciliationTaxCreditsOther

us-gaap:IncomeTaxReconciliationTaxCreditsOther


Income
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value258000.0259000.0258000.0258000.0259000.0258000.0258000.0258000.0259000.0258000.0258000.0258000.0213000.0212000.0213000.0212000.0213000.0212000.0213000.0212000.0213000.0212000.0213000.0212000.0212000.0212000.0212000.0212000.0212000.0216000.0223000.0297000.0149000.0222000.0221000.0220000.0265000.0290000.0
Percentage of IncomeTaxReconciliationTaxCreditsOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncomeTaxReconciliationTaxCreditsResearch

us-gaap:IncomeTaxReconciliationTaxCreditsResearch


Income
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302016-09-302015-09-302014-09-302013-09-30
Value263000.0333000.054000.0612000.0187000.0188000.0227000.0202000.0180000.0148000.0190000.0223000.0-2000.0219000.0520000.0
Percentage of IncomeTaxReconciliationTaxCreditsResearch100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInAccountsPayableAndAccruedLiabilities

us-gaap:IncreaseDecreaseInAccountsPayableAndAccruedLiabilities


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value-6.933111-15.872-7.6920-20.966-3.8664.0889.2514.3134.231-2.7982.4860.7258.108-13.98617-0.5040.399-5.842.343.804-1.109-20.185255.375-12.738-7.7315.5322.078-3.44-4.1571.3075.598-4.12-1.2642.8541.873221.379
Percentage of IncreaseDecreaseInAccountsPayableAndAccruedLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction

us-gaap:IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-31
Value45000.0959000.01246000.01067000.0791000.0951000.0914000.0358000.0330000.0608000.0526000.0422000.0638000.0350000.0235000.0231000.0170000.0252000.0130000.0380000.095000.0359000.0368000.0320000.0256000.0363000.0421000.0419000.0340000.0895000.0274000.0293000.0140000.0216000.0162000.0285000.0284000.0176000.0116000.0-4000.0
Percentage of IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherOperatingAssets

us-gaap:IncreaseDecreaseInOtherOperatingAssets


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value3.8712.596-3.0890.6190.4470.055-0.104-2.742-0.1284.581-1.399-0.094-2.3346.139-0.984-2.1170.0224.231-2.7330.270.7732.373-0.25-0.643-1.27-1.19-0.9043.11-0.437-0.531-2.2423.025-54.1197.8833.0347.473-13.6321.960.63414-20.46
Percentage of IncreaseDecreaseInOtherOperatingAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInReceivables

us-gaap:IncreaseDecreaseInReceivables


Increase
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value20-13.69716-12.73716-14.353-14.265-6.60837-19.2452.1270.6325-18.9878.29-2.68915-2.546-9.1835.1957.478-12.2748.102-5.3711-19.0045.503-4.18122-0.351-3.29713-11.693-4.53220-2.8536.315-11.45430-13.83926
Percentage of IncreaseDecreaseInReceivables100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements us-gaap:AwardType

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements

us-gaap:EmployeeStockOption


Incremental
Period End2021-03-312020-03-31
Value17000.018000.0
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements100.0100.0

us-gaap:PerformanceShares


Incremental
Period End2021-03-312020-03-31
Value143000.0126000.0
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements841.2700.0

us-gaap:RestrictedStock


Incremental
Period End2021-03-312020-03-31
Value85000.083000.0
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements500.0461.1

us-gaap:LongTermPurchaseCommitmentAmount dei:LegalEntity, us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:LongTermPurchaseCommitmentAmount

ottr:OtterTailPowerCompany, ottr:ConstructionPrograms


Long
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302015-03-312014-12-312014-09-30
Value-18.0-127.0-65.0250178616.87038-19.110641-14.0
Percentage of LongTermPurchaseCommitmentAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:OtterTailPowerCompany, ottr:OtpLandEasementsThrough2034


Long
Period End2020-09-30
Value-0.2
Percentage of LongTermPurchaseCommitmentAmount0.2

us-gaap:NetPeriodicDefinedBenefitsExpenseReversalOfExpenseExcludingServiceCostComponent

us-gaap:NetPeriodicDefinedBenefitsExpenseReversalOfExpenseExcludingServiceCostComponent


Net
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value383000.0856000.0842000.0868000.0871000.01128000.01055000.01075000.01035000.01380000.01326000.01386000.01417000.01405000.01403000.01407000.0
Percentage of NetPeriodicDefinedBenefitsExpenseReversalOfExpenseExcludingServiceCostComponent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent


Other
Period End2021-03-312020-03-31
Value-35000.0101000.0
Percentage of OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeAvailableforsaleSecuritiesTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeAvailableforsaleSecuritiesTaxPortionAttributableToParent


Other
Period End2021-03-312020-03-31
Value-10000.027000.0
Percentage of OtherComprehensiveIncomeAvailableforsaleSecuritiesTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToParent


Other
Period End2021-03-312020-03-31
Value-203000.0-138000.0
Percentage of OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent


Other
Period End2021-03-312020-03-31
Value-150000.0-102000.0
Percentage of OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent


Other
Period End2021-03-312020-03-31
Value-53000.0-36000.0
Percentage of OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax


Other
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302012-09-30
Value137000.0138000.0137000.0138000.0176000.0130000.0129000.0130000.0293000.0232000.0233000.0227000.0156000.0157000.0159000.0157000.0158000.0161000.0155000.0154000.0205000.0205000.0207000.0204000.041000.050000.051000.050000.0145000.0146000.0101000.0
Percentage of OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax


Other
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value-17000.0-27000.098000.0101000.0-15000.023000.049000.072000.026000.0-8000.0-10000.0-139000.08000.033000.013000.011000.0-51000.0-25000.018000.047000.0-33000.04000.0-24000.019000.02000.0-24000.023000.0-22000.012000.0-52000.0-19000.043000.02000.063000.0-2000.018000.0
Percentage of OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value115000.0-2547000.075000.0199000.0203000.0-1941000.0119000.0145000.0168000.01663000.0164000.0162000.0-502000.0-2172000.0127000.0109000.0105000.0-224000.072000.0110000.0140000.0397000.0127000.0100000.0141000.0-3003000.06000.0
Percentage of OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-222017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value115000.0-2547000.075000.0199000.0203000.0-1941000.0119000.0145000.0168000.01663000.0164000.0162000.0-502000.0-5601.0105000.0-224000.072000.0110000.0140000.0397000.0127000.0100000.0141000.0-3003000.06000.0
Percentage of OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax


Other
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value2530000.0-102000.0-101000.0-102000.01926000.0-96000.0-96000.0-96000.0-1637000.0-172000.0-172000.0363000.02180000.0-94000.0-96000.0-94000.0173000.0-97000.0-92000.0-93000.0-430000.0-123000.0-124000.0-122000.03005000.0-30000.0-31000.0-30000.0-87000.0-87000.0-87000.0-60000.0-62000.0-61000.0-47000.0-428000.0
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax


Other
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value904000.0-36000.0-36000.0-36000.0677000.0-34000.0-33000.0-34000.0-575000.0-60000.0-61000.0-59000.01455000.0-63000.0-63000.0-63000.0114000.0-64000.0-63000.0-61000.0-285000.0-82000.0-83000.0-82000.02002000.0-20000.0-20000.0-20000.0-58000.0-59000.0-58000.0-41000.0-40000.0-41000.0-32000.0-285000.0
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302016-12-312016-09-30
Value5000.0021000.0-32000.0-2000.0-21000.01000.04000.00-1000.0-4000.00110000.013000.01000.01000.003000.0
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax100.00.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0100.0100.0100.0100.00.0100.0

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value-40000.0-21000.0-13000.092000.0126000.0-40000.030000.066000.091000.032000.0-14000.0-13000.0-66000.025000.052000.021000.017000.0-79000.0-35000.027000.073000.0-50000.06000.0-37000.032000.04000.0-37000.036000.0-17000.019000.0-80000.0-5000.072000.04000.0104000.0-132000.0-3000.031000.0-17000.0
Percentage of OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax


Other
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value-4000.0-7000.026000.027000.0-4000.06000.013000.019000.07000.0-2000.0-3000.0-37000.04000.018000.07000.06000.0-28000.0-13000.09000.026000.0-17000.02000.0-13000.010000.00-13000.013000.0-12000.07000.0-28000.0-11000.029000.02000.041000.0-53000.0-1000.013000.0-7000.0
Percentage of OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherCostAndExpenseOperating

us-gaap:OtherCostAndExpenseOperating


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value13181310111211131313121212111010109.374109.238117.964108.823123.89513159.951121213161717-30.739373213-24.3323232
Percentage of OtherCostAndExpenseOperating100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherNoncashIncomeExpense

us-gaap:OtherNoncashIncomeExpense


Other
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value1569000.0287000.029000.0193000.0-46000.0236000.0-36000.099000.0-375000.0-201000.08000.0-91000.0284000.089000.0-60000.0-44000.05000.0-80000.0-3000.091000.0-15000.053000.0227000.06000.0-206000.0-1904000.039000.01446000.0-182000.054000.0-842000.0-25000.0-368000.0-132000.0-321000.0-1559000.058000.0547000.0-304000.0-2280000.055000.0
Percentage of OtherNoncashIncomeExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsForProceedsFromInvestments

us-gaap:PaymentsForProceedsFromInvestments


Payments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value2.1882.7381.2442.6412.4875.080.773.5181.2581.0481.2221.3830.7191.010.7271.9230.5081.2411.4420.2941.425-0.9951.5342.2713.4920.6370.5090.650.9890.655-0.8980.9231.117-1.0531.3210.2740.603-1.4350.5981.1860.861
Percentage of PaymentsForProceedsFromInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsOfDebtIssuanceCosts

us-gaap:PaymentsOfDebtIssuanceCosts


Payments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value2000.01000.0190000.02000.0177000.0884000.066000.000320000.008000.0433000.0731000.098000.01000.058000.0305000.03000.004000.0340000.0014000.0502000.074000.045000.07000.04000.0010000.089000.0889000.02000.0686000.00101000.0
Percentage of PaymentsOfDebtIssuanceCosts100.0100.0100.0100.0100.0100.0100.00.00.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.00.0100.0

us-gaap:PaymentsOfStockIssuanceCosts

us-gaap:PaymentsOfStockIssuanceCosts


Payments
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302015-12-312015-09-302014-12-312014-09-30
Value25000.0183000.091000.0250000.0124000.0542000.035000.0000090000.0113000.0261000.0102000.0
Percentage of PaymentsOfStockIssuanceCosts100.0100.0100.0100.0100.0100.0100.00.00.00.00.0100.0100.0100.0100.0

us-gaap:PaymentsRelatedToTaxWithholdingForShareBasedCompensation

us-gaap:PaymentsRelatedToTaxWithholdingForShareBasedCompensation


Payments
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value0-3000.02072000.0002730000.0
Percentage of PaymentsRelatedToTaxWithholdingForShareBasedCompensation0.0100.0100.00.00.0100.0

us-gaap:PensionContributions

us-gaap:PensionContributions


Pension
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-03-31
Value10.00.00.00.0110.0120.010.00.00.00.0200.00.00.010.00.00.00.010.00.00.00.0200.00.010.010.0
Percentage of PensionContributions100.00.00.00.0100.00.0100.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.0100.0100.0

us-gaap:PrescriptionDrugBenefitEffectOfSubsidyOnNetPeriodicPostretirementBenefitCost1 us-gaap:RetirementPlanType

us-gaap:PrescriptionDrugBenefitEffectOfSubsidyOnNetPeriodicPostretirementBenefitCost1

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Prescription
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value-281000.0-281000.0-280000.0-281000.045000.045000.044000.045000.0360000.037000.036000.037000.0140000.0141000.0140000.0
Percentage of PrescriptionDrugBenefitEffectOfSubsidyOnNetPeriodicPostretirementBenefitCost1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromIssuanceOfCommonStock

us-gaap:ProceedsFromIssuanceOfCommonStock


Proceeds
Period End2020-12-312020-09-302020-06-302020-03-312019-06-302019-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-30
Value177.994188.3990.00.00.00.0832.3081.9585.05717183.4152.8934.2442.3994.697124.8794.7863.6660.034
Percentage of ProceedsFromIssuanceOfCommonStock100.0100.0100.0100.00.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromIssuanceOfDebt dei:LegalEntity, us-gaap:DebtInstrument

us-gaap:ProceedsFromIssuanceOfDebt

ottr:OtterTailPowerCompany, ottr:Series2020BSeniorUnsecuredNotesDueAugust202030


Proceeds
Period End2020-08-20
Value75
Percentage of ProceedsFromIssuanceOfDebt100.0

us-gaap:ProceedsFromSaleOfProductiveAssets

us-gaap:ProceedsFromSaleOfProductiveAssets


Proceeds
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value3244000.0394000.0664000.01466000.02487000.04408000.0706000.02896000.0509000.0499000.0402000.0967000.0510000.02035000.0289000.01555000.0612000.0670000.03087000.0398000.0682000.0634000.0328000.01336000.01292000.0-795000.078000.02336000.0848000.01012000.0874000.0729000.0-82000.03736000.01824000.0-430000.0826000.01971000.0258000.0-1660000.0710000.0
Percentage of ProceedsFromSaleOfProductiveAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProvisionForDoubtfulAccounts

us-gaap:ProvisionForDoubtfulAccounts


Provision
Period End2020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value474000.0736000.0635000.086000.0216000.0247000.0
Percentage of ProvisionForDoubtfulAccounts100.0100.0100.0100.0100.0100.0

us-gaap:PublicUtilitiesRequestedEquityCapitalStructurePercentage dei:LegalEntity, us-gaap:Range, us-gaap:RegulatoryAgency

us-gaap:PublicUtilitiesRequestedEquityCapitalStructurePercentage

ottr:OtterTailPowerCompany, srt:Maximum, ottr:MinnesotaPublicUtilitiesCommission


Public
Period End2020-07-152020-09-302020-06-302020-03-312019-06-302019-03-312018-12-312018-05-01
Value58.157.5190.0190.56200.58500.585
Percentage of PublicUtilitiesRequestedEquityCapitalStructurePercentage100.0100.0100.0100.00.0100.00.0100.0

ottr:OtterTailPowerCompany, srt:Minimum, ottr:MinnesotaPublicUtilitiesCommission


Public
Period End2020-07-152020-09-302020-06-302020-03-312019-06-302019-03-312018-12-312018-05-01
Value47.547.0250.0150.4600.47900.479
Percentage of PublicUtilitiesRequestedEquityCapitalStructurePercentage81.881.878.981.90.081.90.081.9

us-gaap:PublicUtilitiesRequestedRateIncreaseDecreaseAmount dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType

us-gaap:PublicUtilitiesRequestedRateIncreaseDecreaseAmount

ottr:OtterTailPowerCompany, ottr:The2020GeneralRateCase, ottr:MinnesotaPublicUtilitiesCommission, us-gaap:SubsequentEvent


Public
Period End2020-11-02
Value14
Percentage of PublicUtilitiesRequestedRateIncreaseDecreaseAmount100.0

us-gaap:PublicUtilitiesRequestedRateIncreaseDecreasePercentage dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType

us-gaap:PublicUtilitiesRequestedRateIncreaseDecreasePercentage

ottr:OtterTailPowerCompany, ottr:The2020GeneralRateCase, ottr:MinnesotaPublicUtilitiesCommission, us-gaap:SubsequentEvent


Public
Period End2020-11-02
Value6.77
Percentage of PublicUtilitiesRequestedRateIncreaseDecreasePercentage100.0

us-gaap:RegulatedOperatingRevenueElectricNonNuclear us-gaap:ConsolidationItems

us-gaap:RegulatedOperatingRevenueElectricNonNuclear

us-gaap:IntersegmentElimination


Regulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value-0.01-0.024-0.005-0.016-0.009-0.013-0.017-0.026-0.01-0.007-0.014-0.039-0.005-0.005
Percentage of RegulatedOperatingRevenueElectricNonNuclear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RegulatedOperatingRevenueElectricNonNuclear us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, us-gaap:Retail, ottr:Electric


Regulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value998510610499881131038887108948886
Percentage of RegulatedOperatingRevenueElectricNonNuclear-996050.0-356470.8-2132060.0-655018.8-1104711.1-679576.9-670035.3-398761.5-884330.0-1254785.7-773607.1-242328.2-1779060.0-1725100.0

us-gaap:RegulatedOperatingRevenueElectricNonNuclear us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ottr:Electric


Regulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value11598119114114102128118105103122110103102
Percentage of RegulatedOperatingRevenueElectricNonNuclear-1152230.0-408970.8-2397520.0-714818.8-1270811.1-786492.3-753582.4-454319.2-1054420.0-1481785.7-878321.4-282951.3-2067980.0-2044720.0

us-gaap:RegulatedOperatingRevenueElectricNonNuclear us-gaap:ProductOrService

us-gaap:Electricity


Regulated
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value11598119114114102128118105103122110103102
Percentage of RegulatedOperatingRevenueElectricNonNuclear-1152130.0-408875.0-2397400.0-714737.5-1270711.1-786384.6-753500.0-454219.2-1054320.0-1481700.0-878214.3-282917.9-2067880.0-2044620.0

us-gaap:RevenueNotFromContractWithCustomer us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:RevenueNotFromContractWithCustomer

us-gaap:OperatingSegments, ottr:Electric


Revenue
Period End2021-03-312020-03-31
Value-975000.0-87000.0
Percentage of RevenueNotFromContractWithCustomer100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue

us-gaap:PerformanceShares


Share
Period End2021-03-31
Value38.34
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue100.0

us-gaap:RestrictedStock


Share
Period End2021-03-31
Value42.35
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue110.5

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue

us-gaap:PerformanceShares


Share
Period End2021-03-312020-03-31
Value2500000.03400000.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue100.0100.0

us-gaap:RestrictedStock


Share
Period End2021-03-312020-03-31
Value700000.01300000.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue28.038.2

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue

us-gaap:PerformanceShares


Share
Period End2021-03-31
Value35.73
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue100.0

us-gaap:RestrictedStock


Share
Period End2021-03-31
Value45.93
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue128.5

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate

us-gaap:PerformanceShares


Share
Period End2021-03-312020-03-31
Value32.019.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate

us-gaap:PerformanceShares


Share
Period End2021-03-312020-03-31
Value0.181.42
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate100.0100.0

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage us-gaap:TitleOfIndividual, us-gaap:AwardType, us-gaap:PlanName, us-gaap:Vesting

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage

ottr:Employees, us-gaap:RestrictedStock, ottr:The2014StockIncentivePlan, us-gaap:ShareBasedCompensationAwardTrancheOne


Sharebased
Period End2023-04-08
Value1.0
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage100.0

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue


Stock
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1507000.000-3000.02072000.00002730000.0-1000.0562000.041000.02409000.00040000.01759000.00051000.053000.00175000.0182000.01239000.0131000.00
Percentage of StockRepurchasedAndRetiredDuringPeriodValue100.00.00.0100.0100.00.00.00.0100.0100.0100.0100.0100.00.00.0100.0100.00.00.0100.0100.00.0100.0100.0100.0100.00.0

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1328000.000-3000.01881000.00002454000.0-1000.0503000.036000.02117000.01525000.001000.041000.044000.00142000.0153000.01044000.0108000.00
Percentage of StockRepurchasedAndRetiredDuringPeriodValue88.10.00.0100.090.80.00.00.089.9100.089.587.887.986.70.00.080.483.00.081.184.184.382.40.0

us-gaap:CommonStock


Stock
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value179000.0000191000.0000276000.0059000.05000.0292000.0234000.00-1000.010000.09000.0033000.029000.0195000.023000.00
Percentage of StockRepurchasedAndRetiredDuringPeriodValue11.90.00.0-0.09.20.00.00.010.1-0.010.512.212.113.30.00.019.617.00.018.915.915.717.60.0

us-gaap:UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions

us-gaap:UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions


Unrecognized
Period End2020-12-312020-09-30
Value151000.0-15000.0
Percentage of UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions100.0100.0

us-gaap:UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities

us-gaap:UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities


Unrecognized
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-31
Value-447000.0586000.0000128000.042000.000142000.0044000.000
Percentage of UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities100.0100.00.00.00.0100.0100.00.00.0100.00.0100.00.00.0

us-gaap:UtilitiesOperatingExpenseFuelUsed

us-gaap:UtilitiesOperatingExpenseFuelUsed


Utilities
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value1412118.7881313188.29618151715181416121614149.991512114.183141715122218151720121513191719171816
Percentage of UtilitiesOperatingExpenseFuelUsed100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UtilitiesOperatingExpenseMaintenanceAndOperations

us-gaap:UtilitiesOperatingExpenseMaintenanceAndOperations


Utilities
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value41443233403935393844333739373536
Percentage of UtilitiesOperatingExpenseMaintenanceAndOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UtilitiesOperatingExpenseOther

us-gaap:UtilitiesOperatingExpenseOther


Utilities
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value4.324.4334.3334.1684.13.9613.9653.93.9594.3834.0943.2733.8353836373836363840323237373433393430353228323031272828272729
Percentage of UtilitiesOperatingExpenseOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UtilitiesOperatingExpenseProductsAndServices

us-gaap:UtilitiesOperatingExpenseProductsAndServices


Utilities
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value101828673857788979078939388
Percentage of UtilitiesOperatingExpenseProductsAndServices100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UtilitiesOperatingExpensePurchasedPower

us-gaap:UtilitiesOperatingExpensePurchasedPower


Utilities
Period End2021-03-312020-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value1918789393718684
Percentage of UtilitiesOperatingExpensePurchasedPower100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UtilitiesOperatingExpensePurchasedPower us-gaap:ProductOrService

us-gaap:ElectricityPurchased


Utilities
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value13131817131921229.6641421151316
Percentage of UtilitiesOperatingExpensePurchasedPower0.00.0100.00.00.00.00.028.810.415.40.022.315.519.5

us-gaap:WeightedAverageNumberDilutedSharesOutstandingAdjustment

us-gaap:WeightedAverageNumberDilutedSharesOutstandingAdjustment


Weighted
Period End2021-03-312020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-30
Value245000.0163480.0227200.0232070.0205800.0245840.0282040.0273350.0312810.0287780.0239630.0289920.0173050.0141920.0108260.0219130.0219880.0254760.0242590.0242930.0191560.0202390.0203250.0
Percentage of WeightedAverageNumberDilutedSharesOutstandingAdjustment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:AccountsPayableOutstandingRelatedToCapitalAdditions

ottr:AccountsPayableOutstandingRelatedToCapitalAdditions


Accounts
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-12-312013-09-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value183411261163715164.3381312111013171610131117242023313221212214258.9015.9796.5586.9072.8781.326
Percentage of AccountsPayableOutstandingRelatedToCapitalAdditions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:DebtInstrumentPrepaymentMinimumPercentageOfAggregatePrincipalAmount dei:LegalEntity, us-gaap:DebtInstrument

ottr:DebtInstrumentPrepaymentMinimumPercentageOfAggregatePrincipalAmount

ottr:OtterTailPowerCompany, ottr:The2019NotePurchaseAgreement


Debt
Period End2020-09-302019-10-10
Value10.00.1
Percentage of DebtInstrumentPrepaymentMinimumPercentageOfAggregatePrincipalAmount100.0100.0

ottr:DeferredAndProjectedTransmissionCostsSubjectToFutureRecovery dei:LegalEntity, us-gaap:StatementScenario, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency

ottr:DeferredAndProjectedTransmissionCostsSubjectToFutureRecovery

ottr:OtterTailPowerCompany, srt:ScenarioForecast, ottr:OtterTailPowerCompanysMinnesotaTransmissionCostRecoveryRider, ottr:Minnesota1


Deferred
Period End2020-12-31
Value13
Percentage of DeferredAndProjectedTransmissionCostsSubjectToFutureRecovery100.0

ottr:DeferredTaxAssetsCostOfRemoval

ottr:DeferredTaxAssetsCostOfRemoval


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value2525212131292524
Percentage of DeferredTaxAssetsCostOfRemoval100.0100.0100.0100.0100.0100.0100.0100.0

ottr:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensionAndPostretirementBenefits

ottr:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensionAndPostretirementBenefits


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value4036323138412729
Percentage of DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensionAndPostretirementBenefits100.0100.0100.0100.0100.0100.0100.0100.0

ottr:DeferredTaxLiabilitiesExcessTaxOverBookPension

ottr:DeferredTaxLiabilitiesExcessTaxOverBookPension


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value1817151415136.3538.656
Percentage of DeferredTaxLiabilitiesExcessTaxOverBookPension100.0100.0100.0100.0100.0100.0100.0100.0

ottr:DeferredTaxLiabilitiesRetirementBenefitsRegulatoryAsset

ottr:DeferredTaxLiabilitiesRetirementBenefitsRegulatoryAsset


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value403632313841
Percentage of DeferredTaxLiabilitiesRetirementBenefitsRegulatoryAsset100.0100.0100.0100.0100.0100.0

ottr:DefinedBenefitPlanRegulatoryAssets us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanRegulatoryAssets

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.6812.171.7883.2692.948
Percentage of DefinedBenefitPlanRegulatoryAssets100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1214181813
Percentage of DefinedBenefitPlanRegulatoryAssets472.2689.41012.0579.0460.7

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1371201049998
Percentage of DefinedBenefitPlanRegulatoryAssets5128.75557.25866.73040.13330.4

ottr:DefinedBenefitPlanRegulatoryAssetsNetGainsLosses us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanRegulatoryAssetsNetGainsLosses

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-2681000.0-2170000.0-1768000.0-3229000.0-2890000.0
Percentage of DefinedBenefitPlanRegulatoryAssetsNetGainsLosses100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-137500000.0-120590000.0-104890000.0-99360000.0-98039000.0
Percentage of DefinedBenefitPlanRegulatoryAssetsNetGainsLosses5128.75557.25932.73077.13392.4

ottr:DefinedBenefitPlanRegulatoryAssetsNetPriorServiceCostCredit us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanRegulatoryAssetsNetPriorServiceCostCredit

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312016-12-31
Value-19579000.0-20363000.00-4000.0
Percentage of DefinedBenefitPlanRegulatoryAssetsNetPriorServiceCostCredit100.0100.00.0100.0

ottr:DefinedBenefitPlanUnrecognizedActuarialGainLoss us-gaap:RetirementPlanType

ottr:DefinedBenefitPlanUnrecognizedActuarialGainLoss

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value-32238000.0-35322000.0-18094000.0
Percentage of DefinedBenefitPlanUnrecognizedActuarialGainLoss100.0100.0100.0

ottr:EstimatedLiabilityOfRefundObligation dei:LegalEntity, us-gaap:RegulatoryAgency

ottr:EstimatedLiabilityOfRefundObligation

ottr:OtterTailPowerCompany, ottr:FederalEnergyRegulatoryCommission


Estimated
Period End2020-12-312017-12-312017-09-302017-06-302017-03-312016-12-31
Value3400000.01600000.01600000.01600000.01700000.02700000.0
Percentage of EstimatedLiabilityOfRefundObligation100.0100.0100.0100.0100.0100.0

ottr:OtterTailPowerCompany, ottr:FederalEnergyRegulatoryCommission1111


Estimated
Period End2020-09-30
Value2800.0
Percentage of EstimatedLiabilityOfRefundObligation0.0

ottr:InterestBearingDebtMaximumPercentageOfTotalCapitalization dei:LegalEntity, us-gaap:DebtInstrument

ottr:InterestBearingDebtMaximumPercentageOfTotalCapitalization

ottr:OtterTailPowerCompany, ottr:The2019NotePurchaseAgreement


Interest
Period End2020-09-30
Value60.0
Percentage of InterestBearingDebtMaximumPercentageOfTotalCapitalization100.0

ottr:JointlyOwnedUtilityPlantOwnershipAmountOrDeficitOfConstructionWorkInProgress us-gaap:JointlyOwnedUtilityPlant

ottr:JointlyOwnedUtilityPlantOwnershipAmountOrDeficitOfConstructionWorkInProgress

ottr:BigStonePlant


Jointly
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.5520.3840.3611.0740.023
Percentage of JointlyOwnedUtilityPlantOwnershipAmountOrDeficitOfConstructionWorkInProgress100.0100.0100.0100.0100.0

ottr:CoyoteStation


Jointly
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value0.7320.0832.5880.1580.113
Percentage of JointlyOwnedUtilityPlantOwnershipAmountOrDeficitOfConstructionWorkInProgress28.721.6716.914.7491.3

ottr:LandEasementNonleasePaymentsDueTotal dei:LegalEntity

ottr:LandEasementNonleasePaymentsDueTotal

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value36
Percentage of LandEasementNonleasePaymentsDueTotal100.0

ottr:LandEasementPaymentsToBePaidAfterYearFive dei:LegalEntity

ottr:LandEasementPaymentsToBePaidAfterYearFive

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value29
Percentage of LandEasementPaymentsToBePaidAfterYearFive100.0

ottr:LandEasementPaymentsToBePaidYearFive dei:LegalEntity

ottr:LandEasementPaymentsToBePaidYearFive

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value1436000.0
Percentage of LandEasementPaymentsToBePaidYearFive100.0

ottr:LandEasementPaymentsToBePaidYearFour dei:LegalEntity

ottr:LandEasementPaymentsToBePaidYearFour

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value1410000.0
Percentage of LandEasementPaymentsToBePaidYearFour100.0

ottr:LandEasementPaymentsToBePaidYearOne dei:LegalEntity

ottr:LandEasementPaymentsToBePaidYearOne

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value1900000.0
Percentage of LandEasementPaymentsToBePaidYearOne100.0

ottr:LandEasementPaymentsToBePaidYearThree dei:LegalEntity

ottr:LandEasementPaymentsToBePaidYearThree

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value1386000.0
Percentage of LandEasementPaymentsToBePaidYearThree100.0

ottr:LandEasementPaymentsToBePaidYearTwo dei:LegalEntity

ottr:LandEasementPaymentsToBePaidYearTwo

ottr:OtterTailPowerCompany


Land
Period End2020-12-31
Value1361000.0
Percentage of LandEasementPaymentsToBePaidYearTwo100.0

ottr:LineOfCreditFacilityAmountRestricted

ottr:LineOfCreditFacilityAmountRestricted


Line
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302015-09-302015-06-302015-03-312014-09-302014-06-302013-09-302013-03-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value7.677.671415168.7660.30.30.30.30.30.30.30.050.050.050.050.310.460.7551.0392.6391.8693.9973.7833.95.45.2742.4242.724
Percentage of LineOfCreditFacilityAmountRestricted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:LineOfCreditFacilityAmountRestricted us-gaap:DebtInstrument

ottr:OTPCreditAgreement


Line
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value7.677.671415168.7660.30.30.30.30.30.30.33.054.554.051.051.05
Percentage of LineOfCreditFacilityAmountRestricted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.078.284.376.843.338.5

ottr:LineOfCreditFacilityIncreasedCurrentBorrowingCapacityAccordionProvision us-gaap:DebtInstrument

ottr:LineOfCreditFacilityIncreasedCurrentBorrowingCapacityAccordionProvision

ottr:OTPCreditAgreement


Line
Period End2020-12-31
Value250
Percentage of LineOfCreditFacilityIncreasedCurrentBorrowingCapacityAccordionProvision100.0

ottr:OtterTailCorporationCreditAgreement


Line
Period End2020-12-31
Value290
Percentage of LineOfCreditFacilityIncreasedCurrentBorrowingCapacityAccordionProvision116.0

ottr:MISOIncentiveROE dei:LegalEntity, us-gaap:LitigationCase

ottr:MISOIncentiveROE

ottr:OtterTailPowerCompany, ottr:MISOROEIncentiveSubjectToRecoveryUnderMinnesotaTransmissionCostRecoveryRider


M
Period End2020-09-30
Value2600000.0
Percentage of MISOIncentiveROE100.0

ottr:NetAssetsRestrictedFromDistribution dei:LegalEntity

ottr:NetAssetsRestrictedFromDistribution

ottr:OtterTailPowerCompany


Net
Period End2021-03-312020-12-31
Value671634
Percentage of NetAssetsRestrictedFromDistribution100.0100.0

ottr:NetAssetsRestrictedFromDistribution dei:LegalEntity, us-gaap:RegulatoryAgency

ottr:OtterTailPowerCompany, ottr:MaximumAllowedCapitalizationUnderMinnesotaCapitalStructureFiling


Net
Period End2020-09-30
Value619
Percentage of NetAssetsRestrictedFromDistribution0.0

ottr:NetRegulatoryAssetsLiabilityCurrent

ottr:NetRegulatoryAssetsLiabilityCurrent


Net
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value4.5656.93510146.3565.5427.406168.62610121613121814101215161317241716
Percentage of NetRegulatoryAssetsLiabilityCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:NetRegulatoryAssetsLiabilityNoncurrent

ottr:NetRegulatoryAssetsLiabilityNoncurrent


Net
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value-90.915-97.097-96.374-95.768-108.23-92.963-92.069-91.212-107.041-104.532-103.317384346493845465046494952-3.2179.804
Percentage of NetRegulatoryAssetsLiabilityNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:OtherContractsWithCustomerLiabilityNoncurrent

ottr:OtherContractsWithCustomerLiabilityNoncurrent


Other
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value1914000.02472000.03295000.02885000.02593000.02384000.02117000.01895000.03329000.0
Percentage of OtherContractsWithCustomerLiabilityNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:Ottr_EstimatedLiabilityForFERCOrderedMISOTariffRefundObligation dei:LegalEntity, us-gaap:RegulatoryAgency

ottr:Ottr_EstimatedLiabilityForFERCOrderedMISOTariffRefundObligation

ottr:OtterTailPowerCompany, ottr:FederalEnergyRegulatoryCommission


Ottr_
Period End2021-03-31
Value3700000.0
Percentage of Ottr_EstimatedLiabilityForFERCOrderedMISOTariffRefundObligation100.0

ottr:PercentageOfRequestedAllowedRateOfReturnOnEquity dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType

ottr:PercentageOfRequestedAllowedRateOfReturnOnEquity

ottr:OtterTailPowerCompany, ottr:The2020GeneralRateCase, ottr:MinnesotaPublicUtilitiesCommission, us-gaap:SubsequentEvent


Percentage
Period End2020-11-02
Value10.2
Percentage of PercentageOfRequestedAllowedRateOfReturnOnEquity100.0

ottr:PercentageOfTheRequestedAllowedRateOfReturnOnRateBase dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency, us-gaap:SubsequentEventType

ottr:PercentageOfTheRequestedAllowedRateOfReturnOnRateBase

ottr:OtterTailPowerCompany, ottr:The2020GeneralRateCase, ottr:MinnesotaPublicUtilitiesCommission, us-gaap:SubsequentEvent


Percentage
Period End2020-11-02
Value7.59
Percentage of PercentageOfTheRequestedAllowedRateOfReturnOnRateBase100.0

ottr:PriorityDebtToTotalCapitalization dei:LegalEntity, us-gaap:DebtInstrument

ottr:PriorityDebtToTotalCapitalization

ottr:OtterTailPowerCompany, ottr:The2019NotePurchaseAgreement


Priority
Period End2020-09-30
Value20.0
Percentage of PriorityDebtToTotalCapitalization100.0

ottr:PublicUtilitiesPropertyPlantAndEquipmentElectric

ottr:PublicUtilitiesPropertyPlantAndEquipmentElectric


Public
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value222122112211221221892170216020192000199319811953187018681860184218341824182015901583156015451521150714601438142914231409138013781372134313361332
Percentage of PublicUtilitiesPropertyPlantAndEquipmentElectric100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ottr:TotalDeferredCreditsAndLiabilities

ottr:TotalDeferredCreditsAndLiabilities


Total
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value408400398393384368369369358
Percentage of TotalDeferredCreditsAndLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccountsPayableRelatedPartiesCurrent dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty

us-gaap:AccountsPayableRelatedPartiesCurrent

ottr:OtterTailCorporation, ottr:OtterTailPowerCompany


Accounts
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value7000.07000.07000.06000.010000.0
Percentage of AccountsPayableRelatedPartiesCurrent100.0100.0100.0100.0100.0

us-gaap:AccountsPayableRelatedPartiesCurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Accounts
Period End2020-12-312019-12-312018-12-312017-12-31
Value7000.07000.07000.06000.0
Percentage of AccountsPayableRelatedPartiesCurrent100.0100.0100.0100.0

us-gaap:AccountsReceivableGross

us-gaap:AccountsReceivableGross


Accounts
Period End2021-03-312020-12-312019-12-31
Value137117108
Percentage of AccountsReceivableGross100.0100.0100.0

us-gaap:AccountsReceivableGrossCurrent

us-gaap:AccountsReceivableGrossCurrent


Accounts
Period End2021-03-312020-12-312019-12-31
Value1128779
Percentage of AccountsReceivableGrossCurrent100.0100.0100.0

us-gaap:AccountsReceivableNet

us-gaap:AccountsReceivableNet


Accounts
Period End2021-03-312020-12-312019-12-31
Value134113107
Percentage of AccountsReceivableNet100.0100.0100.0

us-gaap:AccountsReceivableNet us-gaap:ConsolidatedEntities

srt:ParentCompany


Accounts
Period End2020-12-31
Value0.148
Percentage of AccountsReceivableNet0.1

us-gaap:AccountsReceivableRelatedPartiesCurrent dei:LegalEntity

us-gaap:AccountsReceivableRelatedPartiesCurrent

ottr:OtterTailCorporation


Accounts
Period End2020-12-312019-12-31
Value2734000.02144000.0
Percentage of AccountsReceivableRelatedPartiesCurrent100.0100.0

us-gaap:AccountsReceivableRelatedPartiesCurrent dei:LegalEntity, us-gaap:RelatedPartyTransactionsByRelatedParty

ottr:OtterTailCorporation, ottr:OtterTailAssuranceLimited


Accounts
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value36000.084000.050000.025000.071000.0
Percentage of AccountsReceivableRelatedPartiesCurrent1.33.90.00.00.0

ottr:OtterTailCorporation, ottr:OtterTailPowerCompany


Accounts
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2698000.02056000.01877000.02067000.01572000.0
Percentage of AccountsReceivableRelatedPartiesCurrent98.795.90.00.00.0

us-gaap:AccountsReceivableRelatedPartiesCurrent us-gaap:ConsolidatedEntities

srt:ParentCompany


Accounts
Period End2020-12-312019-12-312018-12-312017-12-31
Value2734000.02144000.01931000.02098000.0
Percentage of AccountsReceivableRelatedPartiesCurrent100.0100.00.00.0

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent


Accrual
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312011-06-302010-12-31
Value19181412181713111817151016131017168.39211
Percentage of AccrualForTaxesOtherThanIncomeTaxesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccumulatedDeferredInvestmentTaxCredit

us-gaap:AccumulatedDeferredInvestmentTaxCredit


Accumulated
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1717171718181819191920202121222222232324242425252626272828303131323233333444
Percentage of AccumulatedDeferredInvestmentTaxCredit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivable

us-gaap:AllowanceForDoubtfulAccountsReceivable


Allowance
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value2983000.03215000.02261000.02100000.01681000.01339000.01552000.01691000.01533000.01407000.0
Percentage of AllowanceForDoubtfulAccountsReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AociBeforeTaxAttributableToParent us-gaap:StatementEquityComponents

us-gaap:AociBeforeTaxAttributableToParent

us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLoss


Aoci
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value-11590000.0-11793000.0-8772000.0-6558000.0-9462000.0
Percentage of AociBeforeTaxAttributableToParent100.0100.0100.0100.0100.0

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


Aoci
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value220000.0265000.068000.0-95000.071000.0
Percentage of AociBeforeTaxAttributableToParent-1.9-2.2-0.81.4-0.8

us-gaap:AccumulatedOtherComprehensiveIncome


Aoci
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value-11370000.0-11528000.0-8704000.0-6653000.0-9391000.0
Percentage of AociBeforeTaxAttributableToParent98.197.899.2101.499.2

us-gaap:AociTaxAttributableToParent us-gaap:StatementEquityComponents

us-gaap:AociTaxAttributableToParent

us-gaap:AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLoss


Aoci
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value-3024000.0-3077000.0-2281000.0-1705000.0-2991000.0
Percentage of AociTaxAttributableToParent100.0100.0100.0100.0100.0

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


Aoci
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value46000.056000.014000.0-20000.015000.0
Percentage of AociTaxAttributableToParent-1.5-1.8-0.61.2-0.5

us-gaap:AccumulatedOtherComprehensiveIncome


Aoci
Period End2021-03-312020-12-312019-12-312018-12-312017-12-31
Value-2978000.0-3021000.0-2267000.0-1725000.0-2976000.0
Percentage of AociTaxAttributableToParent98.598.299.4101.299.5

us-gaap:AssetRetirementObligation

us-gaap:AssetRetirementObligation


Asset
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312011-12-312010-12-312009-12-31
Value23129.1178.7198.3418.0847.7214.8084.4024.05
Percentage of AssetRetirementObligation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssetsFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

us-gaap:AssetsFairValueDisclosure

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring


Assets
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value7.0035.7373.2473.013.6563.9494.1232.7942.842.1322.1492.1782.1081.9891.660.8280.8490.7642.8352.2932.1962.6882.7732.550.7130.7020.8010.9760.9621.9152.0921.8462.4714.4724.081129.829.325
Percentage of AssetsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring


Assets
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value9.2099.269.0189.0228.2218.1848.158.0697.6197.4847.5397.1577.167.1387.097.9358.2257.9148.2368.2188.0937.6047.97.8548.0148.3828.6219.0048.9529.6029.35310101427171918
Percentage of AssetsFairValueDisclosure131.5161.4277.7299.7224.9207.2197.7288.8268.3351.0350.8328.6339.7358.9427.1958.3968.81035.9290.5358.4368.5282.9284.9308.01124.01194.01076.3922.5930.6501.4447.1569.3438.9325.3682.3137.6198.4203.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities

us-gaap:AvailableForSaleSecuritiesDebtSecurities


Available
Period End2021-03-312020-12-312019-12-31
Value9209000.09260000.08184000.0
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency, us-gaap:FinancialInstrument

us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring, ottr:GovernmentBackedAndGovernmentSponsoredEnterprisesDebtSecurities


Available
Period End2021-03-312020-12-312019-12-31
Value6808000.06633000.06060000.0
Percentage of AvailableForSaleSecuritiesDebtSecurities73.971.674.0

us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring, us-gaap:CorporateDebtSecurities


Available
Period End2021-03-312020-12-312019-12-31
Value2401000.02627000.02124000.0
Percentage of AvailableForSaleSecuritiesDebtSecurities26.128.426.0

us-gaap:CapitalizationLongtermDebtAndEquity

us-gaap:CapitalizationLongtermDebtAndEquity


Capitalization
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value15121495161615461524147113461334133013181315130411871182117611691175111711291107104810961088108410711061105192496796595996897710551058107410781082
Percentage of CapitalizationLongtermDebtAndEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalizationLongtermDebtAndEquity us-gaap:ConsolidatedEntities

srt:ParentCompany


Capitalization
Period End2020-12-312019-12-312018-12-312017-12-31
Value950861808776
Percentage of CapitalizationLongtermDebtAndEquity63.658.561.365.4

us-gaap:CashAndCashEquivalentsFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:FairValueByMeasurementFrequency

us-gaap:CashAndCashEquivalentsFairValueDisclosure

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring


Cash
Period End2021-03-312020-12-312019-12-312011-09-302011-06-302010-12-31
Value1.8624.0752.3630.5130.8040.8
Percentage of CashAndCashEquivalentsFairValueDisclosure100.0100.0100.0100.0100.0100.0

us-gaap:CashAndCashEquivalentsFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


Cash
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302015-09-302015-03-312013-12-312013-09-302012-12-31
Value1.2121.16344397.884210.9210.9820.8910.8610.6491.036160.8260.5480.1571.155952
Percentage of CashAndCashEquivalentsFairValueDisclosure65.128.50.00.00.0897.10.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:EstimateOfFairValueFairValueDisclosure


Cash
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302015-09-302015-03-312013-12-312013-09-302012-12-31
Value1.2121.16344397.884210.9210.9820.8910.8610.6491.036160.8260.5480.1571.155952
Percentage of CashAndCashEquivalentsFairValueDisclosure65.128.50.00.00.0897.10.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations


Cash
Period End2020-09-302020-06-302019-12-312019-09-302019-06-302018-12-31
Value4439210.9210.9820.861
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations100.0100.0100.0100.0100.0100.0

us-gaap:ContractWithCustomerLiability dei:LegalEntity, us-gaap:RegulatoryAgency

us-gaap:ContractWithCustomerLiability

ottr:OtterTailPowerCompany, ottr:FederalEnergyRegulatoryCommission


Contract
Period End2020-09-30
Value2800000.0
Percentage of ContractWithCustomerLiability100.0

us-gaap:ContractWithCustomerRefundLiability dei:LegalEntity, us-gaap:PublicUtilitiesRegulatoryProceeding, us-gaap:RegulatoryAgency

us-gaap:ContractWithCustomerRefundLiability

ottr:OtterTailPowerCompany, ottr:FirstComplaintPeriod, ottr:FederalEnergyRegulatoryCommission


Contract
Period End2020-09-302020-06-302020-03-312019-12-31
Value100000.0100000.01300000.01300000.0
Percentage of ContractWithCustomerRefundLiability100.0100.0100.0100.0

ottr:OtterTailPowerCompany, ottr:SecondComplaintPeriod, ottr:FederalEnergyRegulatoryCommission


Contract
Period End2020-09-302020-06-302020-03-312019-12-31
Value1400000.01500000.01500000.01500000.0
Percentage of ContractWithCustomerRefundLiability1400.01500.0115.4115.4

us-gaap:DebtInstrumentUnamortizedDiscount

us-gaap:DebtInstrumentUnamortizedDiscount


Debt
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312015-12-312015-09-302014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value2574000.02650000.02726000.02611000.02682000.02587000.02199000.02198000.02284000.02349000.02411000.02477000.02145000.02167000.02242000.02321000.02400000.02221000.01000.01000.01000.01000.01000.03000.03000.04000.04000.04000.04000.04000.04000.05000.05000.0
Percentage of DebtInstrumentUnamortizedDiscount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentUnamortizedDiscount us-gaap:ConsolidatedEntities

ottr:OtterTailPowerCompany


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312016-12-31
Value2408000.02281000.02339000.02231000.01830000.01816000.01890000.01942000.01991000.02045000.01684000.01861000.0
Percentage of DebtInstrumentUnamortizedDiscount88.387.487.286.283.282.682.782.782.682.678.577.5

srt:ParentCompany


Debt
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value318000.0330000.0343000.0356000.0369000.0382000.0394000.0407000.0420000.0432000.0461000.0
Percentage of DebtInstrumentUnamortizedDiscount11.712.612.813.816.817.417.317.317.417.421.5

us-gaap:DebtLongtermAndShorttermCombinedAmount

us-gaap:DebtLongtermAndShorttermCombinedAmount


Debt
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value845813765744695699626633608605611602594590594581583595589576585541547509537526440477438421434483478474475469514
Percentage of DebtLongtermAndShorttermCombinedAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtLongtermAndShorttermCombinedAmount us-gaap:ConsolidatedEntities

ottr:OtterTailPowerCompany


Debt
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312016-12-31
Value700684644644609583532525519510524522486
Percentage of DebtLongtermAndShorttermCombinedAmount82.884.284.286.687.683.485.083.085.384.285.986.783.6

srt:ParentCompany


Debt
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value14512812199851159310789958680
Percentage of DebtLongtermAndShorttermCombinedAmount17.215.815.813.412.416.615.017.014.715.814.113.3

us-gaap:DebtWeightedAverageInterestRate

us-gaap:DebtWeightedAverageInterestRate


Debt
Period End2020-12-312019-12-31
Value1.613.2
Percentage of DebtWeightedAverageInterestRate100.0100.0

us-gaap:DeferredIncomeTaxAssetsNet us-gaap:ConsolidatedEntities

us-gaap:DeferredIncomeTaxAssetsNet

srt:ParentCompany


Deferred
Period End2020-12-312019-12-312018-12-31
Value282521
Percentage of DeferredIncomeTaxAssetsNet100.0100.0100.0

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredIncomeTaxLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value340333321312442437
Percentage of DeferredIncomeTaxLiabilities100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value1.3791.862.4893.2033.865228.38911
Percentage of DeferredTaxAssetsOperatingLossCarryforwards100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsOther

us-gaap:DeferredTaxAssetsOther


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value3423000.0344000.03218000.0668000.07793000.07617000.09630000.07959000.0
Percentage of DeferredTaxAssetsOther100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsPropertyPlantAndEquipment

us-gaap:DeferredTaxAssetsPropertyPlantAndEquipment


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value7.4866.9796.8426.4999.87610
Percentage of DeferredTaxAssetsPropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsRegulatoryAssetsAndLiabilities

us-gaap:DeferredTaxAssetsRegulatoryAssetsAndLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value333533392.422
Percentage of DeferredTaxAssetsRegulatoryAssetsAndLiabilities100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsTaxCreditCarryforwardsOther

us-gaap:DeferredTaxAssetsTaxCreditCarryforwardsOther


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value3531323232324457
Percentage of DeferredTaxAssetsTaxCreditCarryforwardsOther100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value4136333244413735
Percentage of DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxLiabilitiesOther

us-gaap:DeferredTaxLiabilitiesOther


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value102.267.4963.63111107.7097.133
Percentage of DeferredTaxLiabilitiesOther100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxLiabilitiesPropertyPlantAndEquipment

us-gaap:DeferredTaxLiabilitiesPropertyPlantAndEquipment


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312011-12-312010-12-31
Value271268261257371366294269
Percentage of DeferredTaxLiabilitiesPropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPensionPlanLiabilitiesNoncurrent

us-gaap:DefinedBenefitPensionPlanLiabilitiesNoncurrent


Defined
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1031148686879875888898898910998989797959595104939393102505069109107116999897106767573
Percentage of DefinedBenefitPensionPlanLiabilitiesNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanAccumulatedBenefitObligation us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedBenefitObligation

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value385346297316281
Percentage of DefinedBenefitPlanAccumulatedBenefitObligation100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value129.1716.5199.1226.049
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-0.365-0.317-0.107-0.111-0.167
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax-3.0-3.5-1.6-1.2-2.8

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value0.128-0.0820.1460.4480.418
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax1.1-0.92.24.96.9

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-12030000.0-9170000.0-6455000.0-9024000.0-5915000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-21000.0-184000.0107000.0111000.0171000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax0.22.0-1.7-1.2-2.9

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-128000.082000.0-137000.0-439000.0-406000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax1.1-0.92.14.96.9

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1000.01000.064000.098000.0134000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312016-12-31
Value-386000.0-501000.004000.0
Percentage of DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax-38600.0-50100.00.03.0

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.610.03360.04460.03850.046
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.750.03430.04440.03810.0446
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate105.4102.199.699.097.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value2.780.03470.0450.0390.046
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate106.5103.3100.9101.3100.0

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value3.00.0350.0340.02920.03
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease us-gaap:TitleOfIndividual, us-gaap:RetirementPlanType

ottr:ParticipantsAge40To49, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value3.50.0350.035
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease116.7100.0102.9

ottr:ParticipantsAge50AndOlder, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value2.750.02750.0275
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease91.778.680.9

ottr:ParticipantsToAge39, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value4.50.0450.045
Percentage of DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease150.0128.6132.4

us-gaap:DefinedBenefitPlanBenefitObligation us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanBenefitObligation

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value474339423735
Percentage of DefinedBenefitPlanBenefitObligation100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value707171696248
Percentage of DefinedBenefitPlanBenefitObligation146.5162.5180.3164.9167.6136.1

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value428384328352314302
Percentage of DefinedBenefitPlanBenefitObligation894.5875.2827.3833.7842.7845.4

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-31
Value141314
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value16192421
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter117.7142.0170.10.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312017-12-31
Value1000.093882
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter702.50.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-31
Value1.5751.5711.468
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value2.8253.3234.2473.986
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths179.4211.5289.30.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312017-12-31
Value160.014384
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths1049.90.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-31
Value2.6452.6272.635
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value3.2953.7784.7814.327
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive124.6143.8181.40.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312017-12-31
Value180.017041
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive712.90.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-31
Value2.7072.682.214
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value3.1993.724.6984.218
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour118.2138.8212.20.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312017-12-31
Value180.016336
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour676.00.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-31
Value2.7232.2791.618
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value3.0793.6534.4834.133
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree113.1160.3277.10.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312017-12-31
Value170.015666
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree649.80.0

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo

ottr:ExecutiveSurvivorAndSupplementalRetirementPlan


Defined
Period End2020-12-312019-12-312018-12-31
Value2.0491.6811.527
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value2.9553.474.3224.107
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo144.2206.4283.00.0

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312017-12-31
Value170.015022
Percentage of DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo832.10.0

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets

ottr:CashManagementMoneyMarketFund, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value0.3690.0010.0020.0010.003
Percentage of DefinedBenefitPlanFairValueOfPlanAssets100.0100.0100.0100.0100.0

ottr:EmergingMarketsEquityFunds, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-31
Value16139.19715
Percentage of DefinedBenefitPlanFairValueOfPlanAssets4375.61379200.0459850.01582400.0

ottr:InternationalEquitySecurities, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value3530455155
Percentage of DefinedBenefitPlanFairValueOfPlanAssets9649.63065300.02295600.05163600.01863866.7

ottr:LargeCapitalizationEquitySecurities, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value4237476654
Percentage of DefinedBenefitPlanFairValueOfPlanAssets11571.03735700.02359900.06694600.01816100.0

ottr:MixedEquitiesFund, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value69670.0
Percentage of DefinedBenefitPlanFairValueOfPlanAssets18863.76718400.00.0

ottr:SEIDynamicAssetAllocationFund, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1110101413
Percentage of DefinedBenefitPlanFairValueOfPlanAssets3178.61016800.0546450.01437100.0454066.7

ottr:SmallAndMidCapitalizationEquitySecurities, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1613172423
Percentage of DefinedBenefitPlanFairValueOfPlanAssets4366.11344700.0898550.02484800.0767033.3

us-gaap:FixedIncomeSecurities, us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value15914712710087
Percentage of DefinedBenefitPlanFairValueOfPlanAssets43141.514763900.06354900.010037300.02908933.3

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:RetirementPlanType

us-gaap:FairValueInputsLevel1, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value351320258273234
Percentage of DefinedBenefitPlanFairValueOfPlanAssets95246.132024100.012915350.027399900.07810100.0

us-gaap:FairValueMeasuredAtNetAssetValuePerShare, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-31
Value9.229.54
Percentage of DefinedBenefitPlanFairValueOfPlanAssets2498.6954000.0

us-gaap:DefinedBenefitPlanFairValueOfPlanAssets us-gaap:RetirementPlanType

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value360329269285254233
Percentage of DefinedBenefitPlanFairValueOfPlanAssets97744.732978100.013489150.028531900.08478200.00.0

us-gaap:DefinedBenefitPlanFundedStatusOfPlan us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanFundedStatusOfPlan

us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value-67718000.0-55004000.0-58659000.0-67399000.0-60292000.0
Percentage of DefinedBenefitPlanFundedStatusOfPlan100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value6.440.06720.07
Percentage of DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear100.0100.0100.0

us-gaap:DefinedBenefitPlanPlanAssetsTargetAllocationPercentage us-gaap:Range, us-gaap:DefinedBenefitPlanByPlanAssetCategories, us-gaap:RetirementPlanFundingStatus, us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanPlanAssetsTargetAllocationPercentage

srt:Maximum, ottr:BelowInvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan100PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value10.00.10.1
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage100.0100.0100.0

srt:Maximum, ottr:BelowInvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value15.00.150.15
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage150.0150.0150.0

srt:Maximum, ottr:BelowInvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan90PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value15.00.150.15
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage150.0150.0150.0

srt:Maximum, ottr:BelowInvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan95PBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value10.00.10.1
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage100.0100.0100.0

srt:Maximum, ottr:BelowInvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeLessThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value15.00.150.15
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage150.0150.0150.0

srt:Maximum, ottr:InvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan100PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value100.01.01.0
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage1000.01000.01000.0

srt:Maximum, ottr:InvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value50.00.50.5
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage500.0500.0500.0

srt:Maximum, ottr:InvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan90PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value60.00.60.6
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage600.0600.0600.0

srt:Maximum, ottr:InvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan95PBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value73.00.730.73
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage730.0730.0730.0

srt:Maximum, ottr:InvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeLessThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value42.00.420.42
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage420.0420.0420.0

srt:Maximum, ottr:OtherAssetCategories, ottr:PermittedRangeEqualToOrGreaterThan100PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value15.00.150.15
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage150.0150.0150.0

srt:Maximum, ottr:OtherAssetCategories, ottr:PermittedRangeEqualToOrGreaterThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value20.00.20.2
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage200.0200.0200.0

srt:Maximum, ottr:OtherAssetCategories, ottr:PermittedRangeEqualToOrGreaterThan90PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value20.00.20.2
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage200.0200.0200.0

srt:Maximum, ottr:OtherAssetCategories, ottr:PermittedRangeEqualToOrGreaterThan95PBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value15.00.150.15
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage150.0150.0150.0

srt:Maximum, ottr:OtherAssetCategories, ottr:PermittedRangeLessThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value20.00.20.2
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage200.0200.0200.0

srt:Maximum, us-gaap:EquitySecurities, ottr:PermittedRangeEqualToOrGreaterThan100PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value20.00.20.2
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage200.0200.0200.0

srt:Maximum, us-gaap:EquitySecurities, ottr:PermittedRangeEqualToOrGreaterThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value54.00.540.54
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage540.0540.0540.0

srt:Maximum, us-gaap:EquitySecurities, ottr:PermittedRangeEqualToOrGreaterThan90PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value44.00.440.44
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage440.0440.0440.0

srt:Maximum, us-gaap:EquitySecurities, ottr:PermittedRangeEqualToOrGreaterThan95PBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value34.00.340.34
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage340.0340.0340.0

srt:Maximum, us-gaap:EquitySecurities, ottr:PermittedRangeLessThan85PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
Period End2020-12-312019-12-312018-12-31
Value59.00.590.59
Percentage of DefinedBenefitPlanPlanAssetsTargetAllocationPercentage590.0590.0590.0

srt:Minimum, ottr:InvestmentGradeFixedIncomeSecurities, ottr:PermittedRangeEqualToOrGreaterThan100PercentPBO, us-gaap:PensionPlansDefinedBenefit


Defined
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Period End2020-12-312019-12-312018-12-31