CCOI


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

Table of contents



us-gaap:CommonStockValue

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding
us-gaap:StatementScenario

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic
us-gaap:StatementScenario
us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities
us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount

us-gaap:EarningsPerShareBasic
us-gaap:StatementScenario

us-gaap:EarningsPerShareDiluted
us-gaap:StatementScenario

us-gaap:EarningsPerShareBasicAndDiluted

us-gaap:AllocatedShareBasedCompensationExpense
us-gaap:IncomeStatementLocation

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:CostOfGoodsAndServicesSold
us-gaap:StatementScenario

us-gaap:CostsAndExpenses

us-gaap:GainsLossesOnExtinguishmentOfDebt
us-gaap:LongtermDebtType

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign

us-gaap:IncomeTaxExpenseBenefit

us-gaap:InterestExpense

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic
us-gaap:StatementEquityComponents
us-gaap:StatementScenario

us-gaap:OperatingIncomeLoss
us-gaap:StatementScenario

us-gaap:ProfitLoss

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax
us-gaap:ProductOrService
us-gaap:ProductOrService, us-gaap:StatementGeographical
us-gaap:StatementGeographical
us-gaap:StatementScenario

us-gaap:SellingGeneralAndAdministrativeExpense

us-gaap:Assets

us-gaap:Liabilities

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents

us-gaap:AssetsCurrent

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:AccountsReceivableNetCurrent

us-gaap:PrepaidExpenseAndOtherAssetsCurrent

us-gaap:NoncurrentAssets
us-gaap:StatementGeographical

us-gaap:PropertyPlantAndEquipmentGross
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:FiniteLivedIntangibleAssetsByMajorClass, us-gaap:PropertyPlantAndEquipmentByType
us-gaap:PropertyPlantAndEquipmentByType

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:PropertyPlantAndEquipmentByType

us-gaap:PropertyPlantAndEquipmentNet
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:PropertyPlantAndEquipmentByType

us-gaap:DeferredTaxAssetsLiabilitiesNet

us-gaap:AccountsPayableCurrent

us-gaap:AccruedLiabilitiesCurrent

us-gaap:LiabilitiesCurrent

us-gaap:OperatingLeaseLiabilityCurrent

us-gaap:OtherAccruedLiabilitiesCurrent

us-gaap:LongTermDebt
us-gaap:LongtermDebtType
us-gaap:LongtermDebtType
us-gaap:UnsecuredLongTermDebt
us-gaap:LongtermDebtType
us-gaap:SecuredLongTermDebt

us-gaap:OtherLiabilitiesNoncurrent

us-gaap:OperatingLeaseLiabilityNoncurrent

us-gaap:OperatingLeaseLiability

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents

us-gaap:CommonStockValue

us-gaap:AdditionalPaidInCapitalCommonStock

us-gaap:RetainedEarningsAccumulatedDeficit

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:IncreaseDecreaseInAccountsReceivable

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:ProfitLoss

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:RepaymentsOfLongTermDebt

us-gaap:PaymentsOfDividends
us-gaap:StatementScenario
us-gaap:SubsequentEventType

us-gaap:PaymentsForRepurchaseOfCommonStock
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentInterestRateStatedPercentage
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

us-gaap:DeferredTaxLiabilities

us-gaap:DeferredTaxAssetsValuationAllowance
us-gaap:LongtermDebtType
ccoi:AccruedInterestValue

ccoi:DebtInstrumentCovenantPermittedInvestmentsAndPayments
us-gaap:FairValueByFairValueHierarchyLevel
ccoi:FairMarketValueOfEquipmentReceivedInExchange

ccoi:ForeignCurrencyTransactionGainLossUnrealizedOn2024EuroNotes
us-gaap:LongtermDebtType

ccoi:GainLossOnAssetExchangeTransactions

ccoi:IncreaseDecreaseInContractWithCustomerRefundLiability

ccoi:InterestAndOtherIncomeExpense

ccoi:LossOnAmendmentOfFinanceLeases
us-gaap:RelatedPartyTransaction, us-gaap:RelatedPartyTransactionsByRelatedParty
ccoi:OperatingLeaseFixedAnnualRent

ccoi:PropertyPlantAndEquipmentCompensationCostsCapitalized
us-gaap:LongtermDebtType
ccoi:RedemptionPricePer1000AggregatePrincipalAmount
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType
us-gaap:LongtermDebtType
ccoi:RedemptionValue
us-gaap:Range
ccoi:SpeedPerSecondToBandwidthIntensiveUsers

us-gaap:AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease

us-gaap:AllowanceForDoubtfulAccountsReceivableRecoveries

us-gaap:AllowanceForDoubtfulAccountsReceivableWriteOffs

us-gaap:AmortizationOfDebtDiscountPremium

us-gaap:CapitalLeaseObligationsIncurred

us-gaap:CapitalizedContractCostAmortization

us-gaap:CommonStockDividendsPerShareDeclared

us-gaap:ContractWithCustomerLiabilityRevenueRecognized

us-gaap:ContributionOfProperty
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentRedemptionPricePercentage

us-gaap:DividendsCommonStockCash
us-gaap:StatementEquityComponents

us-gaap:EffectOfExchangeRateOnCashAndCashEquivalentsContinuingOperations

us-gaap:ExciseAndSalesTaxes
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType
us-gaap:ExtinguishmentOfDebtAmount

us-gaap:FairValueOfAssetsAcquired

us-gaap:FinanceLeaseInterestExpense

us-gaap:FinanceLeaseInterestPaymentOnLiability

us-gaap:FinanceLeasePrincipalPayments

us-gaap:FinanceLeaseRightOfUseAssetAmortization

us-gaap:ForeignCurrencyTransactionGainLossRealized

us-gaap:ForeignCurrencyTransactionGainLossUnrealized

us-gaap:GainLossOnDispositionOfAssets
us-gaap:LongtermDebtType
us-gaap:GainLossOnRepurchaseOfDebtInstrument
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:GainLossOnSaleOfPropertyPlantEquipment

us-gaap:IncreaseDecreaseInOperatingLiabilities

us-gaap:IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets

us-gaap:InterestAndOtherIncome

us-gaap:LeaseCost

us-gaap:OperatingLeaseCost

us-gaap:OperatingLeasePayments

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent
us-gaap:StatementEquityComponents

us-gaap:ProceedsFromIssuanceOfUnsecuredDebt

us-gaap:ProceedsFromRepaymentsOfNotesPayable

us-gaap:ProceedsFromStockOptionsExercised

us-gaap:ProvisionForDoubtfulAccounts
us-gaap:RelatedPartyTransaction, us-gaap:RelatedPartyTransactionsByRelatedParty
us-gaap:RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
us-gaap:LongtermDebtType
us-gaap:RepaymentsOfSeniorDebt

us-gaap:RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability

us-gaap:RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability
us-gaap:TitleOfIndividual
us-gaap:StockIssuedDuringPeriodSharesShareBasedCompensation
us-gaap:TitleOfIndividual
us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised
us-gaap:StatementEquityComponents

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue
us-gaap:StatementEquityComponents

us-gaap:StockRepurchasedDuringPeriodValue
us-gaap:LongtermDebtType
ccoi:AccruedInterestPer1000AggregatePrincipalAmount
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

ccoi:DeferredTaxAssetsOperatingLeases

ccoi:DeferredTaxLiabilitiesRightOfUseAssets

ccoi:FinanceLeaseLiabilityPaymentsDueAdditional
us-gaap:DebtInstrument, us-gaap:LongtermDebtType
ccoi:FixedChargeCoverageRatio
us-gaap:Range, us-gaap:DebtInstrument
us-gaap:Range, us-gaap:DebtInstrument, us-gaap:LongtermDebtType

ccoi:LeaseRightOfUseAsset
us-gaap:StatementGeographical
ccoi:OperatingLossCarryforwardsNotSubjectToExpiration
us-gaap:Range, us-gaap:DebtInstrument, us-gaap:LongtermDebtType
ccoi:RatioOfAdditionalIndebtednessToNetCapital
us-gaap:LongtermDebtType
ccoi:RedemptionForDebtNoticeIssued
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType
us-gaap:LongtermDebtType
ccoi:UnamortizedDebtIssuanceExpenseCurrent

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent

us-gaap:AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax

us-gaap:AllowanceForDoubtfulAccountsReceivableCurrent

us-gaap:CapitalLeasesFutureMinimumPaymentsDue

us-gaap:CapitalLeasesFutureMinimumPaymentsDueCurrent

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInFiveYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInFourYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInThreeYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInTwoYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueThereafter

us-gaap:CapitalizedContractCostNet
us-gaap:LongtermDebtType, us-gaap:PropertyPlantAndEquipmentByType
us-gaap:ContractualObligation
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentCarryingAmount
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:LongtermDebtType
us-gaap:DebtInstrumentFaceAmount
us-gaap:LongtermDebtType
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:LongtermDebtType
us-gaap:DebtInstrumentFairValue

us-gaap:DebtInstrumentUnamortizedDiscount
us-gaap:LongtermDebtType, us-gaap:PropertyPlantAndEquipmentByType
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentUnamortizedPremium
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentUnamortizedPremiumCurrent
us-gaap:LongtermDebtType
us-gaap:DebtInstrumentUnamortizedPremiumNoncurrent

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredRevenueCurrent

us-gaap:DeferredTaxAssetsGross

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards

us-gaap:DeferredTaxAssetsTaxCreditCarryforwards

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost

us-gaap:DeferredTaxLiabilitiesDeferredExpenseReservesAndAccruals

us-gaap:DeferredTaxLiabilitiesPropertyPlantAndEquipment

us-gaap:DepositsAssetsNoncurrent

us-gaap:EmployeeRelatedLiabilitiesCurrent

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized

us-gaap:FinanceLeaseLiability

us-gaap:FinanceLeaseLiabilityCurrent

us-gaap:FinanceLeaseLiabilityNoncurrent

us-gaap:FinanceLeaseLiabilityPaymentsDue

us-gaap:FinanceLeaseLiabilityPaymentsDueInNextRollingTwelveMonths

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingAfterYearFive

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearFive

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearFour

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearThree

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearTwo

us-gaap:FinanceLeaseLiabilityUndiscountedExcessAmount

us-gaap:FinanceLeaseWeightedAverageDiscountRatePercent

us-gaap:InterestPayableCurrent
us-gaap:LongtermDebtType
us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths
us-gaap:LongtermDebtType
us-gaap:LongTermDebtFairValue

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo

us-gaap:LossContingencyRangeOfPossibleLossPortionNotAccrued

us-gaap:OperatingLeaseWeightedAverageDiscountRatePercent

us-gaap:OperatingLossCarryforwards
us-gaap:StatementGeographical
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:NonmonetaryTransactionType, us-gaap:PropertyPlantAndEquipmentByType
us-gaap:PropertyPlantAndEquipmentFairValueDisclosure
us-gaap:Range, us-gaap:DebtInstrument, us-gaap:LongtermDebtType
us-gaap:RatioOfIndebtednessToNetCapital1

us-gaap:SecuredDebtCurrent
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice
us-gaap:AwardType
us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1

us-gaap:StockRepurchaseProgramAuthorizedAmount1

us-gaap:StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
us-gaap:LongtermDebtType
us-gaap:UnamortizedDebtIssuanceExpense

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount
us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears
us-gaap:ValuationAllowancesAndReservesType
us-gaap:ValuationAllowancesAndReservesBalance

Plots across concepts


IncomeStatement
Profit Loss
Expenses
Income Tax Expense Benefit
Balance Sheet
Stockholders Equity
Assets
Cash And Cash Equivalents At Carrying Value
Current Assets
Prepaid Expense And Other Assets Current
NonCurrent Assets
Property Plant And Equipment Net
PropertyPlantAndEquipmentNet
Property Plant And Equipment Net
Liabilities
Liabilities Current
Current Liabilities
Deferred Revenue Current
Noncurrent Liabilities
Other Liabilities Noncurrent
Stockholders Equity
Retained Earnings Accumulated Deficit
Per Share
Earnings Per Share Diluted
CashFlow
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInOperatingActivities
Profit Loss
NetCashProvidedByUsedInInvestingActivities
Net Cash Provided By Used In Investing Activities
NetCashProvidedByUsedInFinancingActivities
Repayments Of Long Term Debt
Shares
Weighted Average Number Of Diluted Shares Outstanding
DividendsAndRepurchase
Payments For Repurchase Of Common Stock
OperatingLeaseLiability
Operating Lease Liability Current
LesseeOperatingLeaseLiabilityPaymentsDue
Lessee Operating Lease Liability Undiscounted Excess Amount
AccountsReceivable
Allowance For Doubtful Accounts Receivable Current

Tables

  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:CommonStockValue ██▆▆▆▆▆▆▆▃▃▃▃▃▃▃▃▁▁▁▁▁▁▁▃▃▃▃▃▆▆▆▆▆▆▆▆▃0.0480.0480.0470.0470.0470.0470.0470.0470.0470.0460.0460.0460.0460.0460.0460.0460.0460.0450.0450.0450.0450.0450.0450.0450.0460.0460.0460.0460.0460.0470.0470.0470.0470.0470.0470.0470.0470.046NA0.0460.0460.046NANA0.046NANANA
us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding ▁█46.22960346.507258NA45.81571846.68666546.39106646.1459746.01969145.91229145.64423645.80341845.69963545.53647345.29469744.84446945.11860744.98865544.91701444.55808944.77691844.70503744.57193744.55808944.70212745.05450745.1582545.22912545.62907946.29496646.9073648.8005646.82316746.76918446.43567745.49284745.37773245.31380445.24141845.24141845.5825845.55997245.54872544.73185844.73185845.00538744.5852344.52563344.464821
us-gaap:WeightedAverageNumberOfSharesOutstandingBasic █▁46.22960346.067096NA45.81571845.7548845.65856545.55372745.43865645.35432745.22315745.28448145.1058345.01676744.92397344.84446944.76716344.71737244.64964544.32313144.57458344.49189944.4026444.32313144.47472444.77483145.1582545.22912545.62907945.89744946.40973546.30292646.17119446.04069245.53760745.49284745.37773245.31380445.24141845.24141845.04473345.08085945.02150744.73185844.73185844.64638144.5852344.52563344.464821
 us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities us-gaap:EmployeeStockOption▁█0.0360630.077832NANA0.0184960.09307NA0.0376060.0363810.069208NA0.0308360.0433080.077284NA0.0549080.0621750.048534NA0.0756870.0643490.111897NA0.136220.1205330.098102NANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities us-gaap:RestrictedStock▁█0.0280190.39241NANANA0.011884NANA0.037494NANANANA0.078087NA0.0001950.138909NANANANANANA0.6172430.3692430.00336NANANANANANANANANANANA0.7NANANA0.21.2NANANANANA
us-gaap:EarningsPerShareBasic -0.05NA-0.14-0.110.19NA0.159999999999999920.30.160.20.160.180.150.15-0.140.080000000000000020.1NANANANANANANANANA-0.010.00.030.01.140.050.030.01NANANANANANANA0.05NANANANA-0.02NA
 us-gaap:EarningsPerShareBasic us-gaap:StatementScenario ccoi:UnauditedNANA-0.14-0.110.190.2NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:EarningsPerShareDiluted -0.05NA-0.15000000000000002-0.11180.0NA0.160000000000000030.30.16NA0.160.180.14NA-0.140.080000000000000020.1NANANANANA0.060.070.02-0.04-0.010.00.030.01.10.050.030.01NANANANANANANA0.05NANANANA-0.02NA
 us-gaap:EarningsPerShareDiluted us-gaap:StatementScenario ccoi:UnauditedNANA-0.14-0.110.180.2NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:EarningsPerShareBasicAndDiluted NA0.41NANANA0.20.160.30.160.20.160.180.150.15-0.140.080.10.090.060.080.090.080.090.070.02-0.04NA0.00.030.0NA0.050.030.01-0.010.0-0.04-0.05-0.050.120.010.05-0.01-0.010.06-0.01-0.02-0.01
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
 COGS Ratio us-gaap:StatementScenario ccoi:UnauditedNANA143.901142.302140.99140.915140.292136.942134.789134.137NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 Operating Margin us-gaap:StatementScenario ccoi:UnauditedNANA143.901142.302140.99140.915140.292136.942134.789134.137NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
 TTM Greenblatt ROC _ _█▇█▇█▇█▇▆▇▆▆▆▆▆▅▅▅▄▄▅▄▄▄▃▂▃▃▄▃▃▃▃▂▂▂▂▁▁▃▂▂▁▁▁28.21126.29127.37726.03627.57425.8528.03325.79922.02224.422.31122.25521.35420.63720.53417.7219.018.66616.17416.06317.51115.67516.17415.51910.8110.48713.06613.61414.30912.90712.06512.57711.6019.9059.1698.0327.8015.9685.96810.8999.5768.6717.3587.3585.864NANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:AllocatedShareBasedCompensationExpense ▇█▅▇▆▄▄▃▄▁▃▄▃▂6.8747.3075.8466.5226.0825.0754.944.7965.293.4344.4084.8214.6953.784NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:ComprehensiveIncomeNetOfTax ▂▄▂▂▃▃▃▃▃▃▃▃▂▃▁▃▃▃▂▂▂▃▂▂▂▁▂▁▂▂█▃▂▂▂▂▁▂-0.71713.641-0.4280.45311.4775.73410.8168.9928.9227.3924.8447.7460.3549.395-4.9157.4410.485.464-1.4034.1472.2577.428-0.2663.3892.523-8.981-3.41-5.2181.164-0.33753.1944.4631.933-1.4320.9171.407-4.859-0.467NA3.286-3.0372.962.707NANANANANA
us-gaap:CostOfGoodsAndServicesSold ▇█▆▅▅▇▇▆▅▅▆▅▅▆▅▄▁▁56.1857.09254.83154.51953.88655.92155.9955.25354.40754.1555.6654.61554.37954.87553.91853.58451.11550.662NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:CostsAndExpenses ██▇▇▇▇▇▇▇▇▇▆▆▆▆▆▅▅▅▅▅▄▄▄▄▄▃▃▂▂▂▂▂▂▁▁▁▁119.668120.504116.53115.86113.621115.104112.508111.23112.952110.273109.832108.3108.299108.186105.009105.646101.8100.661101.4797.68196.29694.56291.02890.13488.70888.26983.68382.07780.31480.0377.79275.18474.20274.64873.44371.62470.01670.92NA68.19267.79166.90966.102NA63.66863.03461.414NA
us-gaap:GainsLossesOnExtinguishmentOfDebt NA-3.8680.00.0-0.638NANANANANANANANANANANANANANANA-0.587-10.1440.00.00.0-10.144NANANANANANANANANANANANANANANA2.739NANANANANANA
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic ▂█▁▁▅▆▅▇▅▆▆▆▅▅▅▅▅▅▃▅▅▄▅▄▃▁▄▄▄▄▄▄▄▃0.82828.502-4.01-4.08414.11317.78913.23624.45216.33218.75317.64416.65215.44614.13514.98412.2112.6912.3665.1711.97113.2311.38711.7279.3436.078-5.1767.7577.8747.5788.4368.6298.0117.9436.195NANANANANANANANANANANANANANA
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest ▂█▁▁▅▅▅▆▅▅▅▅▄▅▄▄▄▄▃▄▄▄▄▄▃▂▃▃▃▃▃▃▃-2.07126.201-7.264-6.55511.29912.83510.76918.95510.1812.77110.86211.4259.179.9238.4797.0867.9257.6294.5356.3797.6035.7436.3325.5671.535-0.7230.8711.0920.7871.7412.0182.3011.974NANANANANANANANANANANANANANANA
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign ▃▄▃▄▄▂▄▂▁▂▁▂▁▃▁▂▂▂▅▂▂▂▂▃▂█▁▁▁▁▁▂▂▂-2.899-2.301-3.254-2.471-2.814-4.954-2.467-5.497-6.152-5.982-6.782-5.227-6.276-4.212-6.505-5.124-4.765-4.737-0.635-5.592-5.627-5.644-5.395-3.776-4.5434.453-6.886-6.782-6.791-6.695-6.611-5.71-5.969-5.501NANANANANANANANANANANANANANA
us-gaap:IncomeTaxExpenseBenefit ▆▇▆▆▇▇▇▇▇▇▇▇▇▇█▇▇▇▆▇▇▇▇▇▆▇▇▇▆▇▁▆▆▆▇▆▇▆0.4227.35-0.644-1.62.7353.6083.3035.2543.0443.5543.7623.1942.6183.13914.7063.4363.6083.4930.6432.923.3792.3893.8522.4060.6950.8621.2231.276-0.4211.616-50.5810.1790.3670.3331.05-0.4920.752-0.56NA-3.1220.4230.4580.281NA-0.9090.0870.099NA
us-gaap:InterestExpense ▆███▇▇▇▇▆▅▆▅▄▄▄▄▄▄▃▂▂▂▂▂▂▃▄▅▆▃▃▃▂▂▁▁▁▁14.23615.83616.00515.7615.49915.2215.2115.19113.59513.45613.50912.76712.37312.40812.22212.26612.0911.89110.6039.89110.24310.06510.2810.0029.69211.30712.18912.66213.7911.30311.14410.56810.2169.8699.3219.0158.9888.993NA8.8388.9539.1357.585NA4.3424.14.148NA
us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic ▁▄▁▁▃▃▃▃▃▃▃▃▃▃▁▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂█▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂-2.49318.851-6.62-4.9558.5649.2277.46513.7017.1369.2177.18.2316.5526.784-6.2273.654.3174.1362.483.4594.2243.3542.483.1610.84-1.585-0.352-0.1841.2080.12552.5992.1221.6070.361-0.276-0.094-1.791-2.09-2.095.4240.2812.115-0.278-0.2782.584-0.462-0.883-0.57
 us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic us-gaap:StatementEquityComponents us-gaap:RetainedEarnings▂█▁▁▅▅▅▇▅▅▅▅▅▅-2.49318.851-6.62-4.9558.5649.2277.46613.7017.1369.2177.18.2316.5526.784NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic us-gaap:StatementScenario ccoi:UnauditedNANA-6.62-6.5558.5649.2277.46513.7017.1369.217NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:OperatingIncomeLoss █▇█▇█▇█▇▆▇▆▆▆▆▆▅▅▅▅▅▅▅▅▅▃▃▄▄▄▄▄▄▃▃▃▂▂▂▂▃▃▃▂▂▂▁▁▁28.21126.29127.37726.03627.57425.8528.03325.79922.02224.422.31122.25521.35420.63720.53417.7219.018.66616.17416.06317.51115.67516.17415.51910.8110.48713.06613.61414.30912.90712.06512.57711.6019.9059.1698.0327.8015.9685.96810.8999.5768.6717.3587.3585.8643.7492.9812.688
us-gaap:ProfitLoss ▂█▁▁▅▅▅▇▅▅▅▅▅▅-2.49318.851-6.62-4.9558.5649.2277.46613.7017.1369.2177.18.2316.5526.784NANANANANANANANANANANANANANANANANANANANANANANANANANANA2.115NANANANA-0.883NA
us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax ████▇▇▇▇▇▇▇▇▆▆▆▆▆▅▄▄▄▄▄▄▄▄▄▄▄▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▁▁▁147.879146.777143.898142.302140.99140.915140.292136.942134.789134.137132.049130.139129.296128.706125.226122.969119.777117.203105.177103.01798.79997.242105.177103.01798.79997.24296.74995.69194.62392.93789.85987.76185.80384.55382.61279.65677.81776.88876.88879.09377.36775.5873.4673.4669.46166.78364.39562.776
us-gaap:SellingGeneralAndAdministrativeExpense ██▇▇▇▇▆▆▇▆▅▅▆▅▅▅▅▅▅▄▄▄▃▄▄▄▄▄▃▃▂▂▂▂▁▁▁▂41.39241.44239.24439.72239.83939.67536.51735.97138.56635.8633.21833.40933.70433.52331.7532.91531.78831.46131.30630.0529.8229.53227.18127.31828.92529.67727.90427.35326.13926.28522.83221.71921.22621.46519.66819.47319.40121.343NA19.53418.98418.92619.538NA17.79417.65918.091NA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:Assets █▅███▆▇▇▇▄▃▄▃▃▃▃▃▃▃▁▂▂▂▂▂▃▄▄▅▃▄▃▁▁▁▁▁▁1010.747852.9621000.4771000.9141005.401913.625932.124932.344949.065797.003739.85757.319700.229716.453710.588729.86732.439732.675737.892617.622626.378665.096662.816672.906682.388714.046761.775784.461822.787725.247755.101692.253621.372616.237606.531592.885595.217597.289NA597.651578.104587.896NANA376.103NANANA
us-gaap:Liabilities █▇█▇▇▆▆▆▆▅▄▄▄▄▄▄▄▄▄▃▃▃▃▃▃▃▃▃▃▂▂▂▁▁▁▁▁▁1346.8881160.5211293.6431261.6051240.9511135.851135.8031122.8451125.655961.234888.852883.163814.865813.508813.132809.983803.64796.287791.146658.108655.767683.478675.087671.804660.199659.794677.981675.797682.165562.247561.609537.218466.834460.376446.752431.902434.068432.302NA433.65419.465425.642NANA224.302NANANA
us-gaap:LiabilitiesAndStockholdersEquity █▅███▆▇▇▇▄▃▄▃▃▃▃▃▃▃▁▂▂▂▂▂▃▄▄▅▃▄▃▁▁▁▁▁▁1010.747852.9621000.4771000.9141005.401913.625932.124932.344949.065797.003739.85757.319700.229716.453710.588729.86732.439732.675737.892617.622626.378665.096662.816672.906682.388714.046761.775784.461822.787725.247755.101692.253621.372616.237606.531592.885595.217597.289NA597.651578.104587.896NANA376.103NANANA
us-gaap:StockholdersEquity ▁▁▂▂▂▃▃▃▃▃▃▄▄▄▄▄▅▅▅▅▅▅▅▅▆▆▇▇▇██▇▇█████-336.141-307.559-293.166-260.691-235.55-222.225-203.679-190.501-176.59-164.231-149.002-125.844-114.636-97.055-102.544-80.123-71.201-63.612-53.254-40.486-29.389-18.382-12.2711.10222.18954.25283.794108.664140.622163.0193.492155.035154.538155.861159.779160.983161.149164.987NA164.001158.639NANANA151.801NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:AccumulatedTranslationAdjustment▆▅█▅▂▁▃▁▃▂▃▄▅█▆-4.74-6.516-1.306-7.498-12.906-15.819-12.326-15.676-10.967-12.753-10.928-8.672-8.187-1.989-4.6NANANA-17.193NANANA-14.693NANANA-6.462NANANA2.136NANANA0.667NANANANA-0.582NANANANA1.044NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:AdditionalPaidInCapital█▇▆▆▆▅▄▄▃▃▂▂▂▁▁533.049523.913515.867513.454506.391499.455493.178487.396481.734475.275471.331472.817467.007461.154456.696NANANA442.799NANANA434.161NANANA460.576NANANA508.256NANANA497.349NANANANA489.021NANANANA482.737NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:CommonStock██▄▄▄▄▄▄▄▁▁▁▁▁▁0.0480.0480.0470.0470.0470.0470.0470.0470.0470.0460.0460.0460.0460.0460.046NANANA0.045NANANA0.045NANANA0.046NANANA0.047NANANA0.047NANANANA0.046NANANANA0.046NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:RetainedEarnings▁▂▂▃▄▅▅▆▆▆▇▇███-864.498-825.004-807.774-766.694-729.082-705.908-684.578-662.268-647.404-626.799-609.451-590.035-573.502-556.266-554.686NANANA-478.905NANANA-431.784NANANA-370.366NANANA-316.947NANANA-338.284NANANANA-324.484NANANANA-332.026NANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:AssetsCurrent ▇▄▇▇█▇▇▇█▄▅▅▃▃▃▄▄▄▄▁▁▂▂▂▃▄▄▅▆▄▅▄▃▃▃▃▃▃454.555316.27456.337475.353497.116456.562475.728474.373485.993333.85350.337358.507296.736307.549306.118310.31313.152317.838327.623202.28208.047247.393251.339260.036276.527311.969339.641364.254405.821320.654354.271346.321278.942274.202281.253271.069274.731269.527NA273.287258.688264.733NANA88.639NANANA
us-gaap:CashAndCashEquivalentsAtCarryingValue ▇▃▇▇█▇█▇█▄▄▅▃▃▄▄▄▄▄▁▁▂▂▃▃▄▅▅▆▄▅▅▃▃▄▃▃▃373.963237.98371.301393.293417.026375.116399.422396.271409.279259.138276.093284.558224.282236.026247.011250.765256.492263.196274.319148.151154.967196.05203.591207.29224.494260.05287.79311.779349.835263.747304.866304.775237.335234.96247.285232.064237.227232.294NA238.207224.051227.246225.342NA56.28347.83552.435NA
us-gaap:AccountsReceivableNetCurrent █▇█▇▇█▇▇▇▆▇▇▆▆▆▆▅▄▄▄▄▄▃▃▃▃▄▄▄▄▃▃▂▂▁▂▂▁43.75141.23444.18542.05340.5642.96440.48441.29240.68439.25841.70940.99339.48238.01539.09639.11834.75433.69833.59833.48732.37931.52830.71830.99130.97229.76133.08931.7733.50533.12630.62828.70327.17926.83123.9927.9825.65224.915NA25.02924.77426.352NANA23.702NANANA
us-gaap:PrepaidExpenseAndOtherAssetsCurrent ▇▇███▇▇▇▇▇▆▆▆▆▃▃▄▃▃▃▃▃▃▄▄▄▃▃▄▄▃▂▂▂▁▁▁▂36.84137.05640.85140.00739.5338.48235.82236.8136.0335.45432.53532.95632.97233.50820.01120.42721.90620.94419.70620.64220.70119.81517.0321.75521.06122.15818.76220.70522.48123.78118.77712.84314.42812.4119.97811.02511.85212.318NA10.0519.86311.135NANA8.654NANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:NoncurrentAssets █▇█▇▆▄▄▅▅▅▅▅▅▅▅▅▅▄▄▅▅▄▄▄▃▃▄▄▄▃▃▂▂▂▁▁▁▁436.01425.506430.351421.267406.763367.698368.946370.842375.955375.365375.345380.665382.4385.794381.306381.035376.892368.962361.665370.775370.6366.51360.163357.192347.58343.458360.795357.735353.703346.226341.231331.803328.743328.123311.222306.684304.874311.182NA308.043NANA308.043NA280.564NANANA
us-gaap:PropertyPlantAndEquipmentGross NANA1515.867421.251406.747367.6821366.782NANANA1300.503NANANA1233.756NANANA1136.47NANANA1070.111NANANA1047.59NANANA985.084NANANA889.229NANANANA836.047NANANANA759.901NANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass us-gaap:AssetsNANA1032.889NANANA958.612NANANA905.333NANANA850.296NANANA786.55NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:BuildingNANA1.376NANANA1.252NANANA1.277NANANA1.334NANANA1.171NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:EquipmentNANA611.265NANANA566.936NANANA538.761NANANA510.327NANANA476.786NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:LandNANA0.116NANANA0.106NANANA0.108NANANA0.113NANANA0.099NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:LeaseholdImprovementsNANA241.379NANANA227.388NANANA214.495NANANA200.184NANANA182.734NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:OfficeEquipmentNANA19.611NANANA18.169NANANA16.711NANANA14.591NANANA13.735NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:SoftwareAndSoftwareDevelopmentCostsNANA10.609NANANA10.035NANANA9.963NANANA9.701NANANA9.523NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass,us-gaap:PropertyPlantAndEquipmentByType us-gaap:Assets,us-gaap:TechnologyEquipmentNANA148.533NANANA134.726NANANA124.018NANANA114.046NANANA102.502NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType us-gaap:ContractualRightsNANA482.978NANANA408.17NANANA395.17NANANA383.46NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment NANA1085.532NANANA997.853NANANA925.178NANANA852.474NANANA774.829NANANA709.975NANANA686.829NANANA643.891NANANA578.054NANANANA528.069NANANANA479.446NANANA
 us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:FiniteLivedIntangibleAssetsByMajorClass us-gaap:AssetsNANA856.859NANANA790.033NANANA736.356NANANA680.114NANANA621.162NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:PropertyPlantAndEquipmentByType us-gaap:ContractualRightsNANA228.673NANANA207.82NANANA188.822NANANA172.36NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:PropertyPlantAndEquipmentNet █▁▄435.996425.492430.335NANANA368.929370.825375.936375.346375.325381.004382.73385.77381.282381.01376.867368.938361.641370.749370.573366.482360.136357.163347.55343.429360.761357.699353.663346.185341.193331.763328.702328.08311.175306.635304.823311.122NA307.978308.941312.149NANA280.455NANANA
us-gaap:DeferredTaxAssetsLiabilitiesNet NANA170.357NANANA162.866NANANA2.733NANANA17.616NANANA42.241NANANA45.142NANANA52.967NANANA56.182NANANA6.186NANANANA8.784NANANANA3.065NANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:AccountsPayableCurrent ▅▄▂▃▄▄▃▂▃▂▁▁▂▄▃▄▂▄▃▄▆█▄▆▆▇▄▆▇▆▅▄▆▆▅▅▃▆14.60112.199.77511.98312.17113.10211.0759.84911.579.6198.5198.26210.3312.96411.59212.3149.28412.28611.55113.01916.29319.02512.40115.3515.48916.75213.28716.30316.96916.44114.09812.17615.97916.66514.73413.8811.28715.316NA14.1999.97110.938NANA15.979NANANA
us-gaap:AccruedLiabilitiesCurrent ▇▇█▇█▇█▇█▆█▇▇▇▇▇▇▆▇▆▆▅▅▆▅▅▄▃▄▂▃▂▃▂▂▁▂▁48.01449.65651.02947.71452.49249.23951.30149.11551.61545.56451.43146.72847.44746.19847.94747.44949.41245.14647.14941.7943.50240.89638.35545.61640.91338.21432.15131.25734.75427.22131.46523.93527.55224.34626.51920.80725.46820.48NA21.94419.21523.966NANA19.538NANANA
us-gaap:LiabilitiesCurrent ▂█▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▁▁▁▂▁▁▁▁▁▁▁▃▃▃▃▁▁▁▁▁93.726422.70994.44395.247100.06390.1489.69486.22590.21781.55175.30772.27274.95174.47474.52673.55172.33569.24967.91361.95965.88178.91168.90468.63664.58968.25260.03256.5460.064142.347143.694131.911136.15847.71251.7442.10245.97345.537NA47.84339.143.108NANA41.66NANANA
us-gaap:OperatingLeaseLiabilityCurrent ▇▅▅█▅▂▁▂▃▂11.78311.05511.15112.00611.29210.40910.10110.29910.63910.389NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:OtherAccruedLiabilitiesCurrent NANA24.168NANANA23.695NANANA24.02NANANA25.278NANANA47.149NANANA38.355NANANA32.151NANANA31.465NANANA26.519NANANANA21.944NANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:LongTermDebt NANA881.975NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:LongtermDebtType ccoi:SeniorSecuredNotesDue2022NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:UnsecuredLongTermDebt us-gaap:LongtermDebtType ccoi:SeniorUnsecuredNotesOf4.375Due2024████▇▁▁▁412.254406.7425.16406.034388.463147.166150.001145.896NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:UnsecuredLongTermDebt us-gaap:LongtermDebtType us-gaap:SecuredDebtNANA444.492NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:SecuredLongTermDebt us-gaap:LongtermDebtType ccoi:SeniorSecuredNotesDue2026497.025NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:SecuredLongTermDebt us-gaap:LongtermDebtType us-gaap:SecuredDebtNANA444.492444.389444.287NA444.088NANANA443.71NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:OtherLiabilitiesNoncurrent ▅▅▄▄▅▄▄▃▁▁▆▇▇▇▇▇▇▇▇▇▆▇██▆▆▅▅▅▅▅▂▂▂▂▂▃▂19.34619.22114.79216.819.94317.81515.32713.0147.5885.79525.3826.71727.3527.19627.59628.35128.90929.06228.04326.51924.72827.57630.97729.96125.12522.85821.77521.22721.36720.53619.96510.77510.82810.43810.0679.91311.2610.376NA11.1996.0566.232NANA5.86NANANA
us-gaap:OperatingLeaseLiabilityNoncurrent █▇▇▅▄▂▂▁▁▁115.949109.377111.318101.44799.15188.33586.6985.33183.45684.645NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:StockholdersEquity ▁▁▂▂▂▃▃▃▃▃▃▄▄▄▄▄▅▅▅▅▅▅▅▅▆▆▇▇▇██▇▇█████-336.141-307.559-293.166-260.691-235.55-222.225-203.679-190.501-176.59-164.231-149.002-125.844-114.636-97.055-102.544-80.123-71.201-63.612-53.254-40.486-29.389-18.382-12.2711.10222.18954.25283.794108.664140.622163.0193.492155.035154.538155.861159.779160.983161.149164.987NA164.001158.639NANANA151.801NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:AccumulatedTranslationAdjustment▆▅█▅▂▁▃▁▃▂▃▄▅█▆-4.74-6.516-1.306-7.498-12.906-15.819-12.326-15.676-10.967-12.753-10.928-8.672-8.187-1.989-4.6NANANA-17.193NANANA-14.693NANANA-6.462NANANA2.136NANANA0.667NANANANA-0.582NANANANA1.044NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:AdditionalPaidInCapital█▇▆▆▆▅▄▄▃▃▂▂▂▁▁533.049523.913515.867513.454506.391499.455493.178487.396481.734475.275471.331472.817467.007461.154456.696NANANA442.799NANANA434.161NANANA460.576NANANA508.256NANANA497.349NANANANA489.021NANANANA482.737NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:CommonStock██▄▄▄▄▄▄▄▁▁▁▁▁▁0.0480.0480.0470.0470.0470.0470.0470.0470.0470.0460.0460.0460.0460.0460.046NANANA0.045NANANA0.045NANANA0.046NANANA0.047NANANA0.047NANANANA0.046NANANANA0.046NANANA
 us-gaap:StockholdersEquity us-gaap:StatementEquityComponents us-gaap:RetainedEarnings▁▂▂▃▄▅▅▆▆▆▇▇███-864.498-825.004-807.774-766.694-729.082-705.908-684.578-662.268-647.404-626.799-609.451-590.035-573.502-556.266-554.686NANANA-478.905NANANA-431.784NANANA-370.366NANANA-316.947NANANA-338.284NANANANA-324.484NANANANA-332.026NANANA
us-gaap:CommonStockValue ██▆▆▆▆▆▆▆▃▃▃▃▃▃▃▃▁▁▁▁▁▁▁▃▃▃▃▃▆▆▆▆▆▆▆▆▃0.0480.0480.0470.0470.0470.0470.0470.0470.0470.0460.0460.0460.0460.0460.0460.0460.0460.0450.0450.0450.0450.0450.0450.0450.0460.0460.0460.0460.0460.0470.0470.0470.0470.0470.0470.0470.0470.046NA0.0460.0460.046NANA0.046NANANA
us-gaap:AdditionalPaidInCapitalCommonStock █▇▇▇▆▆▅▅▄▄▄▄▃▃▃▂▂▂▂▂▂▁▁▁▂▃▃▄▄▅▆▆▆▆▆▅▅▅533.049523.913515.867513.454506.391499.455493.178487.396481.734475.275471.331472.817467.007461.154456.696452.369447.852445.976442.799442.125440.2436.793434.161431.223440.401456.016460.576467.846480.794496.453508.256505.787503.241500.352497.349494.458491.494490.474NA489.021486.945487.523NANA482.737NANANA
us-gaap:RetainedEarningsAccumulatedDeficit ▁▂▂▂▃▃▃▄▄▄▄▅▅▅▅▅▆▆▆▆▆▆▇▇▇▇▇███████████-864.498-825.004-807.774-766.694-729.082-705.908-684.578-662.268-647.404-626.799-609.451-590.035-573.502-556.266-554.686-526.626-509.397-493.768-478.905-470.758-457.048-444.601-431.784-418.219-406.083-387.952-370.366-355.824-341.848-335.174-316.947-352.34-347.95-343.412-338.284-332.996-328.365-326.574NA-324.484-329.908-330.189NANA-332.026NANANA
us-gaap:StockIssuedDuringPeriodValueNewIssues ▁█0.00.001NANANANA0.00.00.001NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementEquityComponents us-gaap:CommonStock▁█0.00.001NANANANA0.00.00.001NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue █▇▅▆▅▄▃▃▄▁▃▃▃▂8.4767.8316.4317.1476.6665.5595.4155.3115.7143.7714.835.2925.1494.161NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:NetCashProvidedByUsedInOperatingActivities ▆█▅▄▆▃█▄▆▃▆▄▃▃▃▃▃▁▄▁39.74947.10637.57132.9841.31128.45846.09733.44340.63228.63740.72631.74531.27130.17931.3628.78328.04523.51433.87922.833NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:NetCashProvidedByUsedInInvestingActivities ▁▂▂▄▃▄▆▅▅▄▅▅▅▃▆▅▅▄█▇-17.217-15.444-15.86-13.296-13.93-12.866-9.899-12.051-11.72-13.288-10.937-12.107-11.988-14.905-10.618-10.927-12.007-12.249-7.195-8.745NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:NetCashProvidedByUsedInFinancingActivities █▁▄▄▅▄▄▄█▄▄▆▄▄▄▄▄▄█▅112.793-163.667-45.768-44.97713.315-38.572-34.124-32.817120.77-31.809-37.5140.883-29.127-26.791-24.982-24.998-24.516-22.771100.76-20.925NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect █▁▄▄▅▄▄▄█▄▄▆135.983-133.321-21.992-23.73341.91-24.3063.151-13.008150.141-16.955-8.46560.276NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:DeferredIncomeTaxExpenseBenefit ▄▅▄▃▅▅▅▅▅▅▅▅▅▅█▅▅▅▄▅▅▅▁▅▄▄▃▄▄▄-0.9394.497-1.818-2.1531.8142.4392.8734.4542.2592.5723.592.7122.1922.62314.8443.2093.3973.2290.7712.823.312.323-11.5392.3550.6530.822-5.0741.139-0.4571.229NANANANANANANANANANANANANANANANANANA
us-gaap:DepreciationDepletionAndAmortization ███▇▆▅▆▆▆▆▇▆▆▅▅▅▅▄▆▄▄▃▄▃▃▃▃▃▃▃▂▂▂▂▂▁▁▁22.09621.9722.45521.61919.89619.50820.00120.00619.97920.26320.95320.27620.21619.78819.34319.14718.89718.53820.07418.80418.60417.75318.0117.63417.37117.51317.54417.43117.30117.20416.5616.02415.915.87416.12515.6115.50315.239NA15.13615.18814.73414.791NA14.81214.73614.099NA
us-gaap:IncreaseDecreaseInAccountsReceivable ▇▃▆▅▂▇▄▅▆▃▅▆▆▃▄█▅▅▅▅▆▅▅▅▅▃▆▄▅▇▆▆▅▇▁▆▆▄2.33-2.421.61.009-2.6972.79-1.111.0481.259-2.2640.9241.5392.096-1.355-0.1563.9760.384-0.0430.7051.0331.0580.387-0.0010.0080.997-2.1231.857-0.8890.4162.5541.7841.10.2343.175-4.212.041.349-0.426NANANANANANANANANANA
us-gaap:NetCashProvidedByUsedInOperatingActivities ▆█▅▄▆▃█▄▆▃▆▄▃▃▃▃▃▁▄▁39.74947.10637.57132.9841.31128.45846.09733.44340.63228.63740.72631.74531.27130.17931.3628.78328.04523.51433.87922.833NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:ProfitLoss ▂█▁▁▅▅▅▇▅▅▅▅▅▅-2.49318.851-6.62-4.9558.5649.2277.46613.7017.1369.2177.18.2316.5526.784NANANANANANANANANANANANANANANANANANANANANANANANANANANA2.115NANANANA-0.883NA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:NetCashProvidedByUsedInInvestingActivities ▁▂▂▄▃▄▆▅▅▄▅▅▅▃▆▅▅▄█▇-17.217-15.444-15.86-13.296-13.93-12.866-9.899-12.051-11.72-13.288-10.937-12.107-11.988-14.905-10.618-10.927-12.007-12.249-7.195-8.745NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:PaymentsToAcquirePropertyPlantAndEquipment █▇▇▆▆▆▄▅▅▆▄▅▅▇▄▄▅▅▂▃▆▇▁▂▄▆▆▇▇▇▄▄▅▇▄▅▄▅17.21715.44415.8613.29613.9312.8669.89912.05111.7213.28810.93712.10711.98814.90510.61810.92712.00712.2497.1958.74514.2615.0344.9626.83810.86612.91613.02215.40215.98515.62310.09510.16512.45516.31610.28611.18710.57512.289NA10.4249.43713.15312.842NA11.71816.518NANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
us-gaap:NetCashProvidedByUsedInFinancingActivities █▁▄▄▅▄▄▄█▄▄▆▄▄▄▄▄▄█▅112.793-163.667-45.768-44.97713.315-38.572-34.124-32.817120.77-31.809-37.5140.883-29.127-26.791-24.982-24.998-24.516-22.771100.76-20.925NANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:RepaymentsOfLongTermDebt ▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▁▁▁▁█▂▁1.9692.3782.6922.7272.5622.5662.6592.5742.3872.3872.5492.6342.2891.9651.6191.2320.7330.2180.00.019.0192.1840.575NANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:PaymentsOfDividends ██▇▇▇▆▆▆▆▅▅▅▅▅▄▄▄▄▃▃▃▃▃▃▄▃▃▂▁▄37.00136.08134.4632.65731.73830.55729.77628.56527.74126.56526.51624.76423.78822.81921.83320.87919.94618.99918.19917.16916.67116.17116.04515.29618.97216.00114.1913.7927.88218.352NANANANANANANANANANANANANANANANANANA
us-gaap:PaymentsForRepurchaseOfCommonStock NANA4.225NANANANANANANANANANANA0.0NANANA2.826NANANA0.012.16919.1068.11910.55515.917.88814.196NANANANA0.00.01.3NANA0.035NANANANANANANANA
  2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:LongtermDebtType ccoi:SeniorSecuredNotesDue2022NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:LongtermDebtType ccoi:SeniorSecuredNotesDue20263.5e-06NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:LongtermDebtType ccoi:SeniorUnsecuredNotesOf4.375Due20244.375e-06NANANA4.375e-08NANA4.375e-084.375e-08NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue


Common
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value48000.048000.047000.047000.047000.047000.047000.047000.047000.046000.046000.046000.046000.046000.046000.046000.046000.045000.045000.045000.045000.045000.045000.045000.046000.046000.046000.046000.046000.047000.047000.047000.047000.047000.047000.047000.047000.046000.046000.046000.046000.046000.0
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Weighted Average Number Of Diluted Shares Outstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding


Weighted
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
Value4646454646464645454545454544454444444444444444454545454646484646464545454545454545444445444444
Percentage of WeightedAverageNumberOfDilutedSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding us-gaap:StatementScenario

ccoi:Unaudited


Weighted
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value4545464646464545
Percentage of WeightedAverageNumberOfDilutedSharesOutstanding0.0100.0100.0100.0100.0100.0100.0100.0

Weighted Average Number Of Shares Outstanding Basic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic


Weighted
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
Value4646454545454545454545454444444444444444444444444545454546464646454545454545454545444444444444
Percentage of WeightedAverageNumberOfSharesOutstandingBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic us-gaap:StatementScenario

ccoi:Unaudited


Weighted
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value4545454545454545
Percentage of WeightedAverageNumberOfSharesOutstandingBasic0.0100.0100.0100.0100.0100.0100.0100.0

Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount

us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities

us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount

us-gaap:EmployeeStockOption


Antidilutive
Period End2021-06-302021-03-312020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-31
Value36063.077832.018496.093070.037606.036381.069208.030836.043308.077284.054908.062175.048534.075687.064349.0111900.0136220.0120530.098102.0
Percentage of AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RestrictedStock


Antidilutive
Period End2021-06-302021-03-312020-03-312019-06-302018-03-312017-09-302017-06-302015-09-302015-06-302015-03-312012-03-312011-06-302011-03-31
Value28019.0392410.011884.037494.078087.0195.0138910.0617240.0369240.03360.0700000.0200000.01200000.0
Percentage of AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount77.7504.212.8103.1101.00.4223.4453.1306.33.40.00.00.0

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareBasic


Earnings
Period End2021-06-302020-12-312020-09-302020-06-302019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312011-06-302010-06-30
Value-0.05-0.14-0.110.190.160.30.160.20.160.180.150.15-0.140.080.1-0.0100.0301.140.050.030.010.05-0.02
Percentage of EarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.0100.0100.0100.0100.0100.0100.0

us-gaap:EarningsPerShareBasic us-gaap:StatementScenario

ccoi:Unaudited


Earnings
Period End2020-12-312020-09-302020-06-302020-03-31
Value-0.14-0.110.190.2
Percentage of EarningsPerShareBasic100.0100.0100.00.0

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted

us-gaap:EarningsPerShareDiluted


Earnings
Period End2021-06-302020-12-312020-09-302020-06-302019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312011-06-302010-06-30
Value-0.05-0.15-0.11180.00.160.30.160.160.180.14-0.140.080.10.060.070.02-0.04-0.0100.0301.10.050.030.010.05-0.02
Percentage of EarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.0100.0100.0100.0100.0100.0100.0

us-gaap:EarningsPerShareDiluted us-gaap:StatementScenario

ccoi:Unaudited


Earnings
Period End2020-12-312020-09-302020-06-302020-03-31
Value-0.14-0.110.180.2
Percentage of EarningsPerShareDiluted93.3100.00.10.0

Earnings Per Share Basic And Diluted

us-gaap:EarningsPerShareBasicAndDiluted

us-gaap:EarningsPerShareBasicAndDiluted


Earnings
Period End2021-03-312020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
Value0.410.20.160.30.160.20.160.180.150.15-0.140.080.10.090.060.080.090.080.090.070.02-0.0400.0300.050.030.01-0.010-0.04-0.05-0.050.120.010.05-0.01-0.010.06-0.01-0.02-0.01
Percentage of EarningsPerShareBasicAndDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Allocated Share Based Compensation Expense

us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:AllocatedShareBasedCompensationExpense


Allocated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value6.8747.3075.8466.5226.0825.0754.944.7965.293.4344.4084.8214.6953.784
Percentage of AllocatedShareBasedCompensationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax4.65.04.14.64.33.63.53.53.92.63.33.73.62.9

us-gaap:AllocatedShareBasedCompensationExpense us-gaap:IncomeStatementLocation

ccoi:NetworkOperations


Allocated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value0.1362.0760.3160.3460.3050.2520.3060.2820.2260.180.2240.250.2320.189
Percentage of AllocatedShareBasedCompensationExpense2.028.45.45.35.05.06.25.94.35.25.15.24.95.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.11.40.20.20.20.20.20.20.20.10.20.20.20.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:NetworkOperations0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:SellingGeneralAndAdministrativeExpenses


Allocated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value6.7385.2315.536.1765.7784.8234.6344.5155.0633.2544.1844.5714.4633.595
Percentage of AllocatedShareBasedCompensationExpense98.071.694.694.795.095.093.894.195.794.894.994.895.195.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax4.63.63.84.34.13.43.33.33.82.43.23.53.52.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:SellingGeneralAndAdministrativeExpenses0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Comprehensive Income Net Of Tax

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTax


Comprehensive
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value-0.71713-0.4280.453115.734108.9928.9227.3924.8447.7460.3549.395-4.9157.44105.464-1.4034.1472.2577.428-0.2663.3892.523-8.981-3.41-5.2181.164-0.337534.4631.933-1.4320.9171.407-4.859-0.4673.286-3.0372.962.707
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 RevenueFromContractWithCustomerIncludingAssessedTax-0.59.3-0.30.38.14.17.76.66.65.53.76.00.37.3-3.96.18.74.7-1.34.02.37.6-0.33.32.6-9.2-3.5-5.51.2-0.459.25.12.3-1.71.11.8-6.2-0.64.2-3.93.93.7

Cost Of Goods And Services Sold

us-gaap:CostOfGoodsAndServicesSold

us-gaap:CostOfGoodsAndServicesSold


Cost
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value565754545355555554545554545453535150
Percentage of CostOfGoodsAndServicesSold100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax38.038.938.138.338.239.739.940.340.440.442.242.042.142.643.143.642.743.2

us-gaap:CostOfGoodsAndServicesSold us-gaap:StatementScenario

ccoi:Unaudited


Cost
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value5454535555555454
Percentage of CostOfGoodsAndServicesSold100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax38.138.338.239.739.940.340.440.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:Unaudited38.138.338.239.739.940.340.440.4

Costs And Expenses

us-gaap:CostsAndExpenses

us-gaap:CostsAndExpenses


Costs
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value1191201161151131151121111121101091081081081051051011001019796949190888883828080777574747371707068676666636361
Percentage of CostsAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax80.982.181.081.480.681.780.281.283.882.283.283.283.884.183.985.985.085.996.594.897.597.286.587.589.890.886.585.884.986.186.685.786.588.388.989.990.092.286.287.688.590.091.794.495.4

Gains Losses On Extinguishment Of Debt

us-gaap:GainsLossesOnExtinguishmentOfDebt

us-gaap:GainsLossesOnExtinguishmentOfDebt


Gains
Period End2021-03-312020-12-312020-09-302020-06-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312011-06-30
Value-3868000.000-638000.0-587000.0-10144000.0000-10144000.02739000.0
Percentage of GainsLossesOnExtinguishmentOfDebt100.00.00.0100.0100.0100.00.00.00.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-2.60.00.0-0.5-0.6-10.40.00.00.0-10.43.6

us-gaap:GainsLossesOnExtinguishmentOfDebt us-gaap:LongtermDebtType

ccoi:SecuredDebtOne


Gains
Period End2021-06-30
Value-10830000.0
Percentage of GainsLossesOnExtinguishmentOfDebt0.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-7.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:SecuredDebtOne0.0

Income Loss From Continuing Operations Before Income Taxes Domestic

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-31
Value0.82828-4.01-4.08414171324161817161514141212125.17111311119.3436.078-5.1767.7577.8747.5788.4368.6298.0117.9436.195
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.619.4-2.8-2.910.012.69.417.912.114.013.412.811.911.012.09.910.610.64.911.613.411.711.19.16.2-5.38.08.28.09.19.69.19.37.3

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

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value-2.07126-7.264-6.55511121018101210119.179.9238.4797.0867.9257.6294.5356.3797.6035.7436.3325.5671.535-0.7230.8711.0920.7871.7412.0182.3011.974
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-1.417.9-5.0-4.68.09.17.713.87.69.58.28.87.17.76.85.86.66.54.36.27.75.96.05.41.6-0.70.91.10.81.92.22.62.3

Income Loss From Continuing Operations Before Income Taxes Foreign

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-31
Value-2899000.0-2301000.0-3254000.0-2471000.0-2814000.0-4954000.0-2467000.0-5497000.0-6152000.0-5982000.0-6782000.0-5227000.0-6276000.0-4212000.0-6505000.0-5124000.0-4765000.0-4737000.0-635000.0-5592000.0-5627000.0-5644000.0-5395000.0-3776000.0-4543000.04453000.0-6886000.0-6782000.0-6791000.0-6695000.0-6611000.0-5710000.0-5969000.0-5501000.0
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-2.0-1.6-2.3-1.7-2.0-3.5-1.8-4.0-4.6-4.5-5.1-4.0-4.9-3.3-5.2-4.2-4.0-4.0-0.6-5.4-5.7-5.8-5.1-3.7-4.64.6-7.1-7.1-7.2-7.2-7.4-6.5-7.0-6.5

Income Tax Expense Benefit

us-gaap:IncomeTaxExpenseBenefit

us-gaap:IncomeTaxExpenseBenefit


Income
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value0.4227.35-0.644-1.62.7353.6083.3035.2543.0443.5543.7623.1942.6183.139143.4363.6083.4930.6432.923.3792.3893.8522.4060.6950.8621.2231.276-0.4211.616-50.5810.1790.3670.3331.05-0.4920.752-0.56-3.1220.4230.4580.281-0.9090.0870.099
Percentage of IncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.35.0-0.4-1.11.92.62.43.82.32.62.82.52.02.411.72.83.03.00.62.83.42.53.72.30.70.91.31.3-0.41.7-56.30.20.40.41.3-0.61.0-0.7-3.90.50.60.4-1.30.10.2

Interest Expense

us-gaap:InterestExpense

us-gaap:InterestExpense


Interest
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value141516151515151513131312121212121211109.891101010109.69211121213111110109.8699.3219.0158.9888.9938.8388.9539.1357.5854.3424.14.148
Percentage of InterestExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax9.610.811.111.111.010.810.811.110.110.010.29.89.69.69.810.010.110.110.19.610.410.49.89.79.811.612.613.214.612.212.412.011.911.711.311.311.611.711.211.612.110.36.36.16.4

Net Income Loss Available To Common Stockholders Basic

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
Value-2.49318-6.62-4.9558.5649.2277.465137.1369.2177.18.2316.5526.784-6.2273.654.3174.1362.483.4594.2243.3542.483.1610.84-1.585-0.352-0.1841.2080.125522.1221.6070.361-0.276-0.094-1.791-2.09-2.095.4240.2812.115-0.278-0.2782.584-0.462-0.883-0.57
Percentage of NetIncomeLossAvailableToCommonStockholdersBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-1.712.8-4.6-3.56.16.55.310.05.36.95.46.35.15.3-5.03.03.63.52.43.44.33.42.43.10.9-1.6-0.4-0.21.30.158.52.41.90.4-0.3-0.1-2.3-2.7-2.76.90.42.8-0.4-0.43.7-0.7-1.4-0.9

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-2.49318-6.62-4.9558.5649.2277.466137.1369.2177.18.2316.5526.784
Percentage of NetIncomeLossAvailableToCommonStockholdersBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-1.712.8-4.6-3.56.16.55.310.05.36.95.46.35.15.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLossAvailableToCommonStockholdersBasic us-gaap:StatementScenario

ccoi:Unaudited


Net
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value-6.62-6.5558.5649.2277.465137.1369.217
Percentage of NetIncomeLossAvailableToCommonStockholdersBasic100.0132.3100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-4.6-4.66.16.55.310.05.36.9
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:Unaudited-4.6-4.66.16.55.310.05.36.9

Operating Income Loss

us-gaap:OperatingIncomeLoss

us-gaap:OperatingIncomeLoss


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
Value2826272627252825222422222120201719181616171516151010131314121212119.9059.1698.0327.8015.9685.968109.5768.6717.3587.3585.8643.7492.9812.688
Percentage of OperatingIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax19.117.919.018.319.618.320.018.816.318.216.917.116.516.016.414.415.915.915.415.617.716.115.415.110.910.813.514.215.113.913.414.313.511.711.110.110.07.87.813.812.411.510.010.08.45.64.64.3

us-gaap:OperatingIncomeLoss us-gaap:StatementScenario

ccoi:Unaudited


Operating
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value2726272528252224
Percentage of OperatingIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax19.018.319.618.320.018.816.318.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:Unaudited19.018.319.618.320.018.816.318.2

Profit Loss

us-gaap:ProfitLoss

us-gaap:ProfitLoss


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312011-06-302010-06-30
Value-2.49318-6.62-4.9558.5649.2277.466137.1369.2177.18.2316.5526.7842.115-0.883
Percentage of ProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-1.712.8-4.6-3.56.16.55.310.05.36.95.46.35.15.32.8-1.4

Revenue From Contract With Customer Including Assessed Tax

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312012-03-302011-12-312011-09-302011-06-302011-03-312011-03-302010-12-312010-09-302010-06-302010-03-31
Value1471461431421401401401361341341321301291281251221191171051039897105103989796959492898785848279777676797775737369666462
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ProductOrService

ccoi:NonCoreServices


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value0.1390.1070.120.1190.1460.1370.130.1080.1260.1110.1480.1470.1630.1750.190.2060.2110.231
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.10.10.10.10.10.10.10.10.10.10.10.20.20.20.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.10.10.10.10.10.10.10.10.10.10.10.20.20.20.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:NonCoreServices100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OffNetServices


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value363636373737373737363636363635343333
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax24.825.025.526.126.326.526.727.327.627.527.727.827.928.128.528.428.428.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax24.825.025.526.126.326.526.727.327.627.527.727.827.928.128.528.428.428.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OffNetServices100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OnNetServices


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value1111091071051031031029997979593939289878583
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax75.174.974.473.973.673.473.272.672.372.572.272.171.971.871.471.571.571.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax75.174.974.473.973.673.473.272.672.372.572.272.171.971.871.471.571.571.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:ProductOrService, us-gaap:StatementGeographical

ccoi:NonCoreServices, srt:Europe


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.0140.0180.0150.0120.0090.0110.0080.0040.0150.0260.020.0160.014
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:NonCoreServices srt:Europe100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:NonCoreServices, srt:NorthAmerica


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.1250.0890.1050.1070.1370.1260.1220.1040.1110.0850.1280.1310.149
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.10.10.10.10.10.10.10.10.10.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.10.10.10.10.10.10.10.10.10.10.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:NonCoreServices srt:NorthAmerica100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OffNetServices, srt:AsiaPacific


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.2630.2710.2570.240.010.2260.1960.1880.2110.1820.1670.1460.137
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.20.20.20.20.00.20.10.10.20.10.10.10.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.20.20.20.20.00.20.10.10.20.10.10.10.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OffNetServices srt:AsiaPacific100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OffNetServices, srt:Europe


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value4.4944.5924.4714.4224.2164.1434.1314.0534.1134.0264.0053.9453.942
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.03.13.13.13.02.92.93.03.13.03.03.03.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax3.03.13.13.13.02.92.93.03.13.03.03.03.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OffNetServices srt:Europe100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OffNetServices, srt:LatinAmerica


Revenue
Period End2021-06-302021-03-312020-06-302020-03-312019-12-312019-09-302019-06-30
Value0.0490.0160.2260.0110.0070.0050.003
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.20.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.20.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OffNetServices srt:LatinAmerica100.0100.0100.0100.0100.0100.0100.0

ccoi:OffNetServices, srt:NorthAmerica


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value31313132323233333232323232
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.621.722.222.823.123.423.624.224.424.324.524.724.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax21.621.722.222.823.123.423.624.224.424.324.524.724.8
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OffNetServices srt:NorthAmerica100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OffNetServices, srt:SouthAmerica


Revenue
Period End2020-12-312020-09-302019-12-312019-09-30
Value0.0140.0140.0070.005
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.00.00.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OffNetServices srt:SouthAmerica100.0100.0100.0100.0

ccoi:OnNetServices, srt:Africa


Revenue
Period End2021-06-302021-03-312020-12-312020-09-30
Value0.0920.0780.0620.01
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices srt:Africa100.0100.0100.0100.0

ccoi:OnNetServices, srt:AsiaPacific


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value2.4492.1731.9541.7860.4261.4711.3151.181.1280.9910.8760.6760.556
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.71.51.41.30.31.00.90.90.80.70.70.50.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.71.51.41.30.31.00.90.90.80.70.70.50.4
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices srt:AsiaPacific100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OnNetServices, srt:Europe


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value22222119191918171718171718
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax15.115.314.714.013.713.613.113.113.213.613.513.714.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax15.115.314.714.013.713.613.113.113.213.613.513.714.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices srt:Europe100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OnNetServices, srt:LatinAmerica


Revenue
Period End2021-06-302021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value1.0050.8121.6240.320.2440.1390.0710.034
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.70.61.20.20.20.10.10.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.70.61.20.20.20.10.10.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices srt:LatinAmerica100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OnNetServices, srt:NorthAmerica


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value85848382828282807877767574
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax57.657.557.958.158.458.658.958.558.258.158.057.857.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax57.657.557.958.158.458.658.958.558.258.158.057.857.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices srt:NorthAmerica100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:OnNetServices, srt:SouthAmerica


Revenue
Period End2020-12-312020-09-302019-12-312019-09-30
Value0.7120.5990.2440.139
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.50.40.20.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.50.40.20.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:OnNetServices srt:SouthAmerica100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:StatementGeographical

srt:Africa


Revenue
Period End2021-06-302021-03-312020-12-312020-09-30
Value0.0930.0790.0620.01
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.10.10.00.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax srt:Africa100.0100.0100.0100.0

srt:AsiaPacific


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value2.7122.4442.2112.0260.4361.6971.5111.3681.3391.1731.0430.8220.693
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.81.71.51.40.31.21.11.01.00.90.80.60.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax1.81.71.51.40.31.21.11.01.00.90.80.60.5
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax srt:AsiaPacific100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

srt:Europe


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value26272524232322212122212122
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax18.218.417.817.116.716.516.116.016.316.616.616.817.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax18.218.417.817.116.716.516.116.016.316.616.616.817.3
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax srt:Europe100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

srt:LatinAmerica


Revenue
Period End2021-06-302021-03-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value1.0540.8281.850.3310.2510.1440.0740.034
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.70.61.30.20.20.10.10.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.70.61.30.20.20.10.10.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax srt:LatinAmerica100.0100.0100.0100.0100.0100.0100.0100.0

srt:NorthAmerica


Revenue
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value117116115115115115115113111110109107106
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax79.279.380.181.081.782.082.782.882.782.582.682.682.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax79.279.380.181.081.782.082.782.882.782.582.682.682.2
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax srt:NorthAmerica100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

srt:SouthAmerica


Revenue
Period End2020-12-312020-09-302019-12-312019-09-30
Value0.7260.6130.2510.144
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.50.40.20.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax0.50.40.20.1
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax srt:SouthAmerica100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax us-gaap:StatementScenario

ccoi:Unaudited


Revenue
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value143142140140140136134134
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax ccoi:Unaudited100.0100.0100.0100.0100.0100.0100.0100.0

Selling General And Administrative Expense

us-gaap:SellingGeneralAndAdministrativeExpense

us-gaap:SellingGeneralAndAdministrativeExpense


Selling
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value414139393939363538353333333331323131313029292727282927272626222121211919192119181819171718
Percentage of SellingGeneralAndAdministrativeExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax28.028.227.327.928.328.226.026.328.626.725.225.726.126.025.426.826.526.829.829.230.230.425.826.529.330.528.828.627.628.325.424.724.725.423.824.424.927.824.724.525.026.625.626.428.1

Assets

us-gaap:Assets

us-gaap:Assets


Assets
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1010852100010001005913932932949797739757700716710729732732737617626665662672682714761784822725755692621616606592595597597578587376
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Liabilities

us-gaap:Liabilities

us-gaap:Liabilities


Liabilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value134611601293126112401135113511221125961888883814813813809803796791658655683675671660659677675682562561537466460446431434432433419425224
Percentage of Liabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets133.3136.1129.3126.0123.4124.3121.9120.4118.6120.6120.1116.6116.4113.5114.4111.0109.7108.7107.2106.6104.7102.8101.999.896.792.489.086.182.977.574.477.675.174.773.772.872.972.472.672.672.459.6

Liabilities And Stockholders Equity

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:LiabilitiesAndStockholdersEquity


Liabilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1010852100010001005913932932949797739757700716710729732732737617626665662672682714761784822725755692621616606592595597597578587376
Percentage of LiabilitiesAndStockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-312009-12-312008-12-31
Value-336.141-307.559-293.166-260.691-235.55-222.225-203.679-190.501-176.59-164.231-149.002-125.844-114.636-97.055-102.544-80.123-71.201-63.612-53.254-40.486-29.389-18.382-12.2711.102225483108140163193155154155159160161164164158151144150
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-33.3-36.1-29.3-26.0-23.4-24.3-21.9-20.4-18.6-20.6-20.1-16.6-16.4-13.5-14.4-11.0-9.7-8.7-7.2-6.6-4.7-2.8-1.90.23.37.611.013.917.122.525.622.424.925.326.327.227.127.627.427.440.40.00.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedTranslationAdjustment


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value-4.74-6.516-1.306-7.498-12.906-15.819-12.326-15.676-10.967-12.753-10.928-8.672-8.187-1.989-4.6-17.193-14.693-6.4622.1360.667-0.5821.0441.9760.572
Percentage of StockholdersEquity1.42.10.42.95.57.16.18.26.27.87.36.97.12.04.532.3119.7-7.71.10.4-0.40.71.40.4
Percentage of Assets-0.5-0.8-0.1-0.7-1.3-1.7-1.3-1.7-1.2-1.6-1.5-1.1-1.2-0.3-0.6-2.3-2.2-0.80.30.1-0.10.30.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value533523515513506499493487481475471472467461456442434460508497489482475465
Percentage of StockholdersEquity-158.6-170.3-176.0-197.0-215.0-224.8-242.1-255.8-272.8-289.4-316.3-375.7-407.4-475.1-445.4-831.5-3538.1549.7262.7311.3298.2318.0328.9308.1
Percentage of Assets52.761.451.651.350.454.752.952.350.859.663.762.466.764.464.360.065.560.567.382.081.8128.40.00.0
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

us-gaap:CommonStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value0.0480.0480.0470.0470.0470.0470.0470.0470.0470.0460.0460.0460.0460.0460.0460.0450.0450.0460.0470.0470.0460.0460.0450.044
Percentage of StockholdersEquity-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.1-0.40.10.00.00.00.00.00.0
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: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

us-gaap:RetainedEarnings


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value-864.498-825.004-807.774-766.694-729.082-705.908-684.578-662.268-647.404-626.799-609.451-590.035-573.502-556.266-554.686-478.905-431.784-370.366-316.947-338.284-324.484-332.026-332.695-315.544
Percentage of StockholdersEquity257.2268.2275.5294.1309.5317.7336.1347.6366.6381.7409.0468.9500.3573.1540.9899.33518.7-442.0-163.8-211.7-197.9-218.7-230.3-209.0
Percentage of Assets-85.5-96.7-80.7-76.6-72.5-77.3-73.4-71.0-68.2-78.6-82.4-77.9-81.9-77.6-78.1-64.9-65.1-48.6-42.0-55.8-54.3-88.30.00.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Assets Current

us-gaap:AssetsCurrent

us-gaap:AssetsCurrent


Assets
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value45431645647549745647547448533335035829630730631031331732720220824725126027631133936440532035434627827428127127426927325826488
Percentage of AssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets45.037.145.647.549.450.051.050.951.241.947.447.342.442.943.142.542.843.444.432.833.237.237.938.640.543.744.646.449.344.246.950.044.944.546.445.746.245.145.744.745.023.6

Cash And Cash Equivalents At Carrying Value

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:CashAndCashEquivalentsAtCarryingValue


Cash
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-312008-12-31
Value3732373713934173753993964092592762842242362472502562632741481541962032072242602873113492633043042372342472322372322382242272255647525571
Percentage of CashAndCashEquivalentsAtCarryingValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets37.027.937.139.341.541.142.942.543.132.537.337.632.032.934.834.435.035.937.224.024.729.530.730.832.936.437.839.742.536.440.444.038.238.140.839.139.938.939.938.838.70.015.00.00.00.00.0

Accounts Receivable Net Current

us-gaap:AccountsReceivableNetCurrent

us-gaap:AccountsReceivableNetCurrent


Accounts
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value434144424042404140394140393839393433333332313030302933313333302827262327252425242623
Percentage of AccountsReceivableNetCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets4.34.84.44.24.04.74.34.44.34.95.65.45.65.35.55.44.74.64.65.45.24.74.64.64.54.24.34.04.14.64.14.14.44.44.04.74.34.24.24.34.56.3

Prepaid Expense And Other Assets Current

us-gaap:PrepaidExpenseAndOtherAssetsCurrent

us-gaap:PrepaidExpenseAndOtherAssetsCurrent


Prepaid
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value363740403938353636353232323320202120192020191721212218202223181214129.978111112109.863118.654
Percentage of PrepaidExpenseAndOtherAssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets3.64.34.14.03.94.23.83.93.84.44.44.44.74.72.82.83.02.92.73.33.33.02.63.23.13.12.52.62.73.32.51.92.32.01.61.92.02.11.71.71.92.3

Noncurrent Assets

us-gaap:NoncurrentAssets

us-gaap:NoncurrentAssets


Noncurrent
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-03-312010-12-31
Value436425430421406367368370375375375380382385381381376368361370370366360357347343360357353346341331328328311306304311308308280
Percentage of NoncurrentAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets43.149.943.042.140.540.239.639.839.647.150.750.354.653.853.752.251.550.449.060.059.255.154.353.150.948.147.445.643.047.745.247.952.953.251.351.751.252.151.50.074.6

us-gaap:NoncurrentAssets us-gaap:StatementGeographical

ccoi:EuropeAndOther


Noncurrent
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value1271231231151051009997102999999
Percentage of NoncurrentAssets29.229.028.727.426.027.327.026.227.226.526.626.0
Percentage of Assets12.614.512.411.610.511.010.710.410.812.513.514.0
Percentage of Assets ccoi:EuropeAndOther0.00.00.00.00.00.00.00.00.00.00.00.0

srt:NorthAmerica


Noncurrent
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302018-12-31
Value308302306305301267269273273275
Percentage of NoncurrentAssets70.871.071.372.674.072.773.073.872.873.4
Percentage of Assets30.535.430.730.530.029.228.929.328.837.2
Percentage of Assets srt:NorthAmerica0.00.00.00.00.00.00.00.00.00.0

Property Plant And Equipment Gross

us-gaap:PropertyPlantAndEquipmentGross

us-gaap:PropertyPlantAndEquipmentGross


Property
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value1515421406367136613001233113610701047985889836759
Percentage of PropertyPlantAndEquipmentGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets151.542.140.540.2146.6175.8173.6154.0161.4137.5130.5146.6139.9202.0

us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:Assets


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1032958905850786
Percentage of PropertyPlantAndEquipmentGross68.170.169.668.969.2
Percentage of Assets103.2102.8122.4119.7106.6
Percentage of Assets us-gaap:Assets0.00.00.00.00.0

us-gaap:PropertyPlantAndEquipmentGross us-gaap:FiniteLivedIntangibleAssetsByMajorClass, us-gaap:PropertyPlantAndEquipmentByType

us-gaap:Assets, us-gaap:Building


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1.3761.2521.2771.3341.171
Percentage of PropertyPlantAndEquipmentGross0.10.10.10.10.1
Percentage of Assets0.10.10.20.20.2
Percentage of Assets us-gaap:Assets us-gaap:Building0.00.00.00.00.0

us-gaap:Assets, us-gaap:Equipment


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value611566538510476
Percentage of PropertyPlantAndEquipmentGross40.341.541.441.442.0
Percentage of Assets61.160.872.871.864.6
Percentage of Assets us-gaap:Assets us-gaap:Equipment0.00.00.00.00.0

us-gaap:Assets, us-gaap:Land


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value0.1160.1060.1080.1130.099
Percentage of PropertyPlantAndEquipmentGross0.00.00.00.00.0
Percentage of Assets0.00.00.00.00.0
Percentage of Assets us-gaap:Assets us-gaap:Land0.00.00.00.00.0

us-gaap:Assets, us-gaap:LeaseholdImprovements


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value241227214200182
Percentage of PropertyPlantAndEquipmentGross15.916.616.516.216.1
Percentage of Assets24.124.429.028.224.8
Percentage of Assets us-gaap:Assets us-gaap:LeaseholdImprovements0.00.00.00.00.0

us-gaap:Assets, us-gaap:OfficeEquipment


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value1918161413
Percentage of PropertyPlantAndEquipmentGross1.31.31.31.21.2
Percentage of Assets2.01.92.32.11.9
Percentage of Assets us-gaap:Assets us-gaap:OfficeEquipment0.00.00.00.00.0

us-gaap:Assets, us-gaap:SoftwareAndSoftwareDevelopmentCosts


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value10109.9639.7019.523
Percentage of PropertyPlantAndEquipmentGross0.70.70.80.80.8
Percentage of Assets1.11.11.31.41.3
Percentage of Assets us-gaap:Assets us-gaap:SoftwareAndSoftwareDevelopmentCosts0.00.00.00.00.0

us-gaap:Assets, us-gaap:TechnologyEquipment


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value148134124114102
Percentage of PropertyPlantAndEquipmentGross9.89.99.59.29.0
Percentage of Assets14.814.516.816.013.9
Percentage of Assets us-gaap:Assets us-gaap:TechnologyEquipment0.00.00.00.00.0

us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType

us-gaap:ContractualRights


Property
Period End2020-12-312019-12-312018-12-312017-12-31
Value482408395383
Percentage of PropertyPlantAndEquipmentGross31.929.930.431.1
Percentage of Assets48.343.853.454.0
Percentage of Assets us-gaap:ContractualRights0.00.00.00.0

Accumulated Depreciation Depletion And Amortization Property Plant And Equipment

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment


Accumulated
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value1085997925852774709686643578528479
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets108.5107.1125.0120.0105.0107.190.285.395.388.4127.5

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:Assets


Accumulated
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value856790736680621
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment78.979.279.679.880.2
Percentage of Assets85.684.899.595.784.2
Percentage of Assets us-gaap:Assets0.00.00.00.00.0

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment us-gaap:PropertyPlantAndEquipmentByType

us-gaap:ContractualRights


Accumulated
Period End2020-12-312019-12-312018-12-312017-12-31
Value228207188172
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment21.120.820.420.2
Percentage of Assets22.922.325.524.3
Percentage of Assets us-gaap:ContractualRights0.00.00.00.0

Property Plant And Equipment Net

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:PropertyPlantAndEquipmentNet


Property
Period End2021-06-302021-03-312020-12-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value435425430368370375375375381382385381381376368361370370366360357347343360357353346341331328328311306304311307308312280
Percentage of PropertyPlantAndEquipmentNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets43.149.943.039.639.839.647.150.750.354.753.853.752.251.550.449.060.059.255.154.353.150.948.147.445.643.047.745.247.952.953.251.351.751.252.151.553.453.174.6

us-gaap:PropertyPlantAndEquipmentNet us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:Assets


Property
Period End2020-12-312019-12-312018-12-312017-12-312016-12-31
Value176168168170165
Percentage of PropertyPlantAndEquipmentNet40.945.745.044.645.7
Percentage of Assets17.618.122.823.922.4
Percentage of Assets us-gaap:Assets0.00.00.00.00.0

us-gaap:PropertyPlantAndEquipmentNet us-gaap:PropertyPlantAndEquipmentByType

us-gaap:ContractualRights


Property
Period End2020-12-312019-12-312018-12-312017-12-31
Value254200206211
Percentage of PropertyPlantAndEquipmentNet59.154.355.055.4
Percentage of Assets25.421.527.929.7
Percentage of Assets us-gaap:ContractualRights0.00.00.00.0

Deferred Tax Assets Liabilities Net

us-gaap:DeferredTaxAssetsLiabilitiesNet

us-gaap:DeferredTaxAssetsLiabilitiesNet


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value1701622.73317424552566.1868.7843.065
Percentage of DeferredTaxAssetsLiabilitiesNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets17.017.50.42.55.76.87.07.41.01.50.8

Accounts Payable Current

us-gaap:AccountsPayableCurrent

us-gaap:AccountsPayableCurrent


Accounts
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value14129.775111213119.849119.6198.5198.262101211129.284121113161912151516131616161412151614131115149.9711015
Percentage of AccountsPayableCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.41.41.01.21.21.41.21.11.21.21.21.11.51.81.61.71.31.71.62.12.62.91.92.32.32.31.72.12.12.31.91.82.62.72.42.31.92.62.41.71.94.2

Accrued Liabilities Current

us-gaap:AccruedLiabilitiesCurrent

us-gaap:AccruedLiabilitiesCurrent


Accrued
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value484951475249514951455146474647474945474143403845403832313427312327242620252021192319
Percentage of AccruedLiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets4.85.85.14.85.25.45.55.35.45.77.06.26.86.46.76.56.76.26.46.86.96.15.86.86.05.44.24.04.23.84.23.54.44.04.43.54.33.43.73.34.15.2

Liabilities Current

us-gaap:LiabilitiesCurrent

us-gaap:LiabilitiesCurrent


Liabilities
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value934229495100908986908175727474747372696761657868686468605660142143131136475142454547394341
Percentage of LiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets9.349.69.49.510.09.99.69.29.510.210.29.510.710.410.510.19.99.59.210.010.511.910.410.29.59.67.97.27.319.619.019.121.97.78.57.17.77.68.06.87.311.1

Operating Lease Liability Current

us-gaap:OperatingLeaseLiabilityCurrent

us-gaap:OperatingLeaseLiabilityCurrent


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value11111112111010101010
Percentage of OperatingLeaseLiabilityCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.21.31.11.21.11.11.11.11.11.3

Other Accrued Liabilities Current

us-gaap:OtherAccruedLiabilitiesCurrent

us-gaap:OtherAccruedLiabilitiesCurrent


Other
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value24232425473832312621
Percentage of OtherAccruedLiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets2.42.53.23.66.45.84.24.24.43.7

Long Term Debt

us-gaap:LongTermDebt

us-gaap:LongTermDebt


Long
Period End2020-12-31
Value881
Percentage of LongTermDebt100.0
Percentage of Assets88.2

us-gaap:LongTermDebt us-gaap:LongtermDebtType

ccoi:SeniorSecuredNotesDue2022


Long
Period End2021-05-31
Value284
Percentage of LongTermDebt0.0
Percentage of Assets0.0
Percentage of Assets ccoi:SeniorSecuredNotesDue20220.0

Unsecured Long Term Debt

us-gaap:UnsecuredLongTermDebt us-gaap:LongtermDebtType

us-gaap:UnsecuredLongTermDebt

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Unsecured
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value412406425406388147150145
Percentage of UnsecuredLongTermDebt100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets40.847.742.540.638.616.116.115.6
Percentage of Assets ccoi:SeniorUnsecuredNotesOf4.375Due20240.00.00.00.00.00.00.00.0

us-gaap:SecuredDebt


Unsecured
Period End2020-12-31
Value444
Percentage of UnsecuredLongTermDebt104.5
Percentage of Assets44.4
Percentage of Assets us-gaap:SecuredDebt0.0

Secured Long Term Debt

us-gaap:SecuredLongTermDebt us-gaap:LongtermDebtType

us-gaap:SecuredLongTermDebt

ccoi:SeniorSecuredNotesDue2026


Secured
Period End2021-06-30
Value497
Percentage of SecuredLongTermDebt100.0
Percentage of Assets49.2
Percentage of Assets ccoi:SeniorSecuredNotesDue20260.0

us-gaap:SecuredDebt


Secured
Period End2020-12-312020-09-302020-06-302019-12-312018-12-31
Value444444444444443
Percentage of SecuredLongTermDebt0.00.00.00.00.0
Percentage of Assets44.444.444.247.660.0
Percentage of Assets us-gaap:SecuredDebt0.00.00.00.00.0

Other Liabilities Noncurrent

us-gaap:OtherLiabilitiesNoncurrent

us-gaap:OtherLiabilitiesNoncurrent


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value19191416191715137.5885.795252627272728282928262427302925222121212019101010109.9131110116.0566.2325.86
Percentage of OtherLiabilitiesNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.92.31.51.72.01.91.61.40.80.73.43.53.93.83.93.93.94.03.84.33.94.14.74.53.73.22.92.72.62.82.61.61.71.71.71.71.91.71.91.01.11.6

Operating Lease Liability Noncurrent

us-gaap:OperatingLeaseLiabilityNoncurrent

us-gaap:OperatingLeaseLiabilityNoncurrent


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value115109111101998886858384
Percentage of OperatingLeaseLiabilityNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets11.512.811.110.19.99.79.39.28.810.6

Operating Lease Liability

us-gaap:OperatingLeaseLiability

us-gaap:OperatingLeaseLiability


Operating
Period End2021-03-312020-12-312020-09-30
Value120122113
Percentage of OperatingLeaseLiability100.0100.0100.0
Percentage of Assets14.112.211.3

Lessee Operating Lease Liability Payments Due

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue


Lessee
Period End2021-03-312020-12-312020-09-30
Value191196179
Percentage of LesseeOperatingLeaseLiabilityPaymentsDue100.0100.0100.0
Percentage of Assets22.519.618.0

Lessee Operating Lease Liability Undiscounted Excess Amount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount


Lessee
Period End2021-03-312020-12-312020-09-30
Value717366
Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount100.0100.0100.0
Percentage of Assets8.37.46.6

Stockholders Equity

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-312009-12-312008-12-31
Value-336.141-307.559-293.166-260.691-235.55-222.225-203.679-190.501-176.59-164.231-149.002-125.844-114.636-97.055-102.544-80.123-71.201-63.612-53.254-40.486-29.389-18.382-12.2711.102225483108140163193155154155159160161164164158151144150
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-33.3-36.1-29.3-26.0-23.4-24.3-21.9-20.4-18.6-20.6-20.1-16.6-16.4-13.5-14.4-11.0-9.7-8.7-7.2-6.6-4.7-2.8-1.90.23.37.611.013.917.122.525.622.424.925.326.327.227.127.627.427.440.40.00.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedTranslationAdjustment


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value-4.74-6.516-1.306-7.498-12.906-15.819-12.326-15.676-10.967-12.753-10.928-8.672-8.187-1.989-4.6-17.193-14.693-6.4622.1360.667-0.5821.0441.9760.572
Percentage of StockholdersEquity1.42.10.42.95.57.16.18.26.27.87.36.97.12.04.532.3119.7-7.71.10.4-0.40.71.40.4
Percentage of Assets-0.5-0.8-0.1-0.7-1.3-1.7-1.3-1.7-1.2-1.6-1.5-1.1-1.2-0.3-0.6-2.3-2.2-0.80.30.1-0.10.30.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value533523515513506499493487481475471472467461456442434460508497489482475465
Percentage of StockholdersEquity-158.6-170.3-176.0-197.0-215.0-224.8-242.1-255.8-272.8-289.4-316.3-375.7-407.4-475.1-445.4-831.5-3538.1549.7262.7311.3298.2318.0328.9308.1
Percentage of Assets52.761.451.651.350.454.752.952.350.859.663.762.466.764.464.360.065.560.567.382.081.8128.40.00.0
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

us-gaap:CommonStock


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value0.0480.0480.0470.0470.0470.0470.0470.0470.0470.0460.0460.0460.0460.0460.0460.0450.0450.0460.0470.0470.0460.0460.0450.044
Percentage of StockholdersEquity-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.1-0.40.10.00.00.00.00.00.0
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: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

us-gaap:RetainedEarnings


Stockholders
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-312008-12-31
Value-864.498-825.004-807.774-766.694-729.082-705.908-684.578-662.268-647.404-626.799-609.451-590.035-573.502-556.266-554.686-478.905-431.784-370.366-316.947-338.284-324.484-332.026-332.695-315.544
Percentage of StockholdersEquity257.2268.2275.5294.1309.5317.7336.1347.6366.6381.7409.0468.9500.3573.1540.9899.33518.7-442.0-163.8-211.7-197.9-218.7-230.3-209.0
Percentage of Assets-85.5-96.7-80.7-76.6-72.5-77.3-73.4-71.0-68.2-78.6-82.4-77.9-81.9-77.6-78.1-64.9-65.1-48.6-42.0-55.8-54.3-88.30.00.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue


Common
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value48000.048000.047000.047000.047000.047000.047000.047000.047000.046000.046000.046000.046000.046000.046000.046000.046000.045000.045000.045000.045000.045000.045000.045000.046000.046000.046000.046000.046000.047000.047000.047000.047000.047000.047000.047000.047000.046000.046000.046000.046000.046000.0
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Additional Paid In Capital Common Stock

us-gaap:AdditionalPaidInCapitalCommonStock

us-gaap:AdditionalPaidInCapitalCommonStock


Additional
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value533523515513506499493487481475471472467461456452447445442442440436434431440456460467480496508505503500497494491490489486487482
Percentage of AdditionalPaidInCapitalCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets52.761.451.651.350.454.752.952.350.859.663.762.466.764.464.362.061.160.960.071.670.365.765.564.164.563.960.559.658.468.567.373.181.081.282.083.482.682.181.884.282.9128.4

Retained Earnings Accumulated Deficit

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:RetainedEarningsAccumulatedDeficit


Retained
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value-864.498-825.004-807.774-766.694-729.082-705.908-684.578-662.268-647.404-626.799-609.451-590.035-573.502-556.266-554.686-526.626-509.397-493.768-478.905-470.758-457.048-444.601-431.784-418.219-406.083-387.952-370.366-355.824-341.848-335.174-316.947-352.34-347.95-343.412-338.284-332.996-328.365-326.574-324.484-329.908-330.189-332.026
Percentage of RetainedEarningsAccumulatedDeficit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-85.5-96.7-80.7-76.6-72.5-77.3-73.4-71.0-68.2-78.6-82.4-77.9-81.9-77.6-78.1-72.2-69.5-67.4-64.9-76.2-73.0-66.8-65.1-62.2-59.5-54.3-48.6-45.4-41.5-46.2-42.0-50.9-56.0-55.7-55.8-56.2-55.2-54.7-54.3-57.1-56.2-88.3

Stock Issued During Period Value New Issues

us-gaap:StockIssuedDuringPeriodValueNewIssues

us-gaap:StockIssuedDuringPeriodValueNewIssues


Stock
Period End2021-06-302021-03-312019-12-312019-09-302019-06-30
Value01000.0001000.0
Percentage of StockIssuedDuringPeriodValueNewIssues0.0100.00.00.0100.0
Percentage of Assets0.00.00.00.00.0

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:StatementEquityComponents

us-gaap:CommonStock


Stock
Period End2021-06-302021-03-312019-12-312019-09-302019-06-30
Value01000.0001000.0
Percentage of StockIssuedDuringPeriodValueNewIssues0.0100.00.00.0100.0
Percentage of Assets0.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.0

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

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue


Adjustments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value8.4767.8316.4317.1476.6665.5595.4155.3115.7143.7714.835.2925.1494.161
Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Adjustments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value8.4767.8316.4317.1476.6665.5595.4145.3115.7143.7714.835.2925.1494.161
Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value3947373241284633402840313130312828233322
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax26.932.126.123.229.320.232.924.430.121.330.824.424.223.425.023.423.420.132.222.2

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-17217000.0-15444000.0-15860000.0-13296000.0-13930000.0-12866000.0-9899000.0-12051000.0-11720000.0-13288000.0-10937000.0-12107000.0-11988000.0-14905000.0-10618000.0-10927000.0-12007000.0-12249000.0-7195000.0-8745000.0
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-11.6-10.5-11.0-9.3-9.9-9.1-7.1-8.8-8.7-9.9-8.3-9.3-9.3-11.6-8.5-8.9-10.0-10.5-6.8-8.5

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value112-163.667-45.768-44.97713-38.572-34.124-32.817120-31.809-37.5140-29.127-26.791-24.982-24.998-24.516-22.771100-20.925
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax76.3-111.5-31.8-31.69.4-27.4-24.3-24.089.6-23.7-28.431.4-22.5-20.8-19.9-20.3-20.5-19.495.8-20.3

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

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect


Cash
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value135-133.321-21.992-23.73341-24.3063.151-13.008150-16.955-8.46560
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax92.0-90.8-15.3-16.729.7-17.22.2-9.5111.4-12.6-6.446.3

Deferred Income Tax Expense Benefit

us-gaap:DeferredIncomeTaxExpenseBenefit

us-gaap:DeferredIncomeTaxExpenseBenefit


Deferred
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value-0.9394.497-1.818-2.1531.8142.4392.8734.4542.2592.5723.592.7122.1922.623143.2093.3973.2290.7712.823.312.323-11.5392.3550.6530.822-5.0741.139-0.4571.229
Percentage of DeferredIncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Depreciation Depletion And Amortization

us-gaap:DepreciationDepletionAndAmortization

us-gaap:DepreciationDepletionAndAmortization


Depreciation
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-30
Value222122211919202019202020201919191818201818171817171717171717161615151615151515151414141414
Percentage of DepreciationDepletionAndAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Increase Decrease In Accounts Receivable

us-gaap:IncreaseDecreaseInAccountsReceivable

us-gaap:IncreaseDecreaseInAccountsReceivable


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value2330000.0-2420000.01600000.01009000.0-2697000.02790000.0-1110000.01048000.01259000.0-2264000.0924000.01539000.02096000.0-1355000.0-156000.03976000.0384000.0-43000.0705000.01033000.01058000.0387000.0-1000.08000.0997000.0-2123000.01857000.0-889000.0416000.02554000.01784000.01100000.0234000.03175000.0-4210000.02040000.01349000.0-426000.0
Percentage of IncreaseDecreaseInAccountsReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value3947373241284633402840313130312828233322
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax26.932.126.123.229.320.232.924.430.121.330.824.424.223.425.023.423.420.132.222.2

Profit Loss

us-gaap:ProfitLoss

us-gaap:ProfitLoss


Profit
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312011-06-302010-06-30
Value-2.49318-6.62-4.9558.5649.2277.466137.1369.2177.18.2316.5526.7842.115-0.883
Percentage of ProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-1.712.8-4.6-3.56.16.55.310.05.36.95.46.35.15.32.8-1.4

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-17217000.0-15444000.0-15860000.0-13296000.0-13930000.0-12866000.0-9899000.0-12051000.0-11720000.0-13288000.0-10937000.0-12107000.0-11988000.0-14905000.0-10618000.0-10927000.0-12007000.0-12249000.0-7195000.0-8745000.0
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax-11.6-10.5-11.0-9.3-9.9-9.1-7.1-8.8-8.7-9.9-8.3-9.3-9.3-11.6-8.5-8.9-10.0-10.5-6.8-8.5

Payments To Acquire Property Plant And Equipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment


Payments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value1715151313129.89912111310121114101012127.1958.74514154.9626.8381012131515151010121610111012109.43713121116
Percentage of PaymentsToAcquirePropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


Net
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value112-163.667-45.768-44.97713-38.572-34.124-32.817120-31.809-37.5140-29.127-26.791-24.982-24.998-24.516-22.771100-20.925
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerIncludingAssessedTax76.3-111.5-31.8-31.69.4-27.4-24.3-24.089.6-23.7-28.431.4-22.5-20.8-19.9-20.3-20.5-19.495.8-20.3

Repayments Of Long Term Debt

us-gaap:RepaymentsOfLongTermDebt

us-gaap:RepaymentsOfLongTermDebt


Repayments
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-31
Value1.9692.3782.6922.7272.5622.5662.6592.5742.3872.3872.5492.6342.2891.9651.6191.2320.7330.2180.00.0192.1840.575
Percentage of RepaymentsOfLongTermDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0100.0100.0100.0

Payments Of Dividends

us-gaap:PaymentsOfDividends

us-gaap:PaymentsOfDividends


Payments
Period End2021-06-302021-03-312020-12-042020-12-312020-09-302020-05-052020-06-302020-03-272020-03-312019-12-092019-12-312019-09-092019-09-302019-06-302019-03-312018-12-312018-09-302018-06-012018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-112015-09-302015-06-122015-06-302015-03-262015-03-312014-12-122014-12-312014-09-192014-09-302014-06-182014-06-302014-03-272014-03-312013-12-202013-09-252013-06-182013-03-152012-12-122012-09-12
Value3736333432313130302929282827262624242322212019181817161616151518181616141413137.8827.8821818176.5126.1455.4895.0124.537
Percentage of PaymentsOfDividends100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsOfDividends us-gaap:StatementScenario

srt:ScenarioForecast


Payments
Period End2021-09-032021-05-282020-09-04
Value373532
Percentage of PaymentsOfDividends0.00.00.0

us-gaap:PaymentsOfDividends us-gaap:SubsequentEventType

us-gaap:SubsequentEvent


Payments
Period End2021-03-262019-03-29
Value3426
Percentage of PaymentsOfDividends0.00.0

Payments For Repurchase Of Common Stock

us-gaap:PaymentsForRepurchaseOfCommonStock

us-gaap:PaymentsForRepurchaseOfCommonStock


Payments
Period End2020-12-312017-12-312016-12-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312012-12-312012-09-302012-06-302011-12-31
Value4.2250.02.8260.012198.119101517140.00.01.30.035
Percentage of PaymentsForRepurchaseOfCommonStock100.00.0100.00.0100.0100.0100.0100.0100.0100.0100.00.00.0100.0100.0

Debt Instrument Interest Rate Stated Percentage

us-gaap:DebtInstrumentInterestRateStatedPercentage us-gaap:LongtermDebtType

us-gaap:DebtInstrumentInterestRateStatedPercentage

ccoi:SeniorSecuredNotesDue2022


Debt
Period End2021-05-31
Value5.375
Percentage of DebtInstrumentInterestRateStatedPercentage100.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.0
Percentage of LongTermDebtAndCapitalLeaseObligations ccoi:SeniorSecuredNotesDue20220.0

ccoi:SeniorSecuredNotesDue2026


Debt
Period End2021-06-30
Value3.5
Percentage of DebtInstrumentInterestRateStatedPercentage0.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.0
Percentage of LongTermDebtAndCapitalLeaseObligations ccoi:SeniorSecuredNotesDue20260.0

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2021-06-302020-06-302019-09-302019-06-302019-06-25
Value4.3750.043750.043750.043750.04375
Percentage of DebtInstrumentInterestRateStatedPercentage0.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations0.00.00.00.00.0
Percentage of LongTermDebtAndCapitalLeaseObligations ccoi:SeniorUnsecuredNotesOf4.375Due20240.00.00.00.00.0

Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

us-gaap:EmployeeStockOption


Share
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value54.0946.2141.0136.3732.3528.3725.4119.3614.8713.17
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Liabilities

us-gaap:DeferredTaxLiabilities

us-gaap:DeferredTaxLiabilities


Deferred
Period End2020-12-312019-12-31
Value9658000.09399000.0
Percentage of DeferredTaxLiabilities100.0100.0

Deferred Tax Assets Valuation Allowance

us-gaap:DeferredTaxAssetsValuationAllowance

us-gaap:DeferredTaxAssetsValuationAllowance


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value150131126129210213345354347337343
Percentage of DeferredTaxAssetsValuationAllowance100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:AccruedInterestValue us-gaap:LongtermDebtType

ccoi:AccruedInterestValue

ccoi:SeniorSecuredNotesDue2022


Accrued
Period End2021-04-06
Value400000.0
Percentage of AccruedInterestValue100.0

ccoi:DebtInstrumentCovenantPermittedInvestmentsAndPayments

ccoi:DebtInstrumentCovenantPermittedInvestmentsAndPayments


Debt
Period End2021-06-302021-03-312020-12-312016-03-31
Value20557-38.627
Percentage of DebtInstrumentCovenantPermittedInvestmentsAndPayments100.0100.0100.0100.0

ccoi:FairMarketValueOfEquipmentReceivedInExchange us-gaap:FairValueByFairValueHierarchyLevel

ccoi:FairMarketValueOfEquipmentReceivedInExchange

us-gaap:FairValueInputsLevel3


Fair
Period End2020-09-302020-06-302019-09-302019-06-30
Value0.20.70.30.5
Percentage of FairMarketValueOfEquipmentReceivedInExchange100.0100.0100.0100.0

ccoi:ForeignCurrencyTransactionGainLossUnrealizedOn2024EuroNotes

ccoi:ForeignCurrencyTransactionGainLossUnrealizedOn2024EuroNotes


Foreign
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-30
Value-5.2818-19.17-17.315-3.422.904-4.0686.1620.177
Percentage of ForeignCurrencyTransactionGainLossUnrealizedOn2024EuroNotes100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:ForeignCurrencyTransactionGainLossUnrealizedOn2024EuroNotes us-gaap:LongtermDebtType

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Foreign
Period End2021-06-302020-09-302020-06-302019-09-302019-06-30
Value5.3-17.3-3.46.20.2
Percentage of ForeignCurrencyTransactionGainLossUnrealizedOn2024EuroNotes-100.499.999.4100.6113.0

ccoi:GainLossOnAssetExchangeTransactions

ccoi:GainLossOnAssetExchangeTransactions


Gain
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value0.00.10.20.10.20.10.10.50.1240.4160.3430.1170.3520.41.02.1240.6680.74.41.9462.4391.1230.6383.9563.0173.1142.6652.235
Percentage of GainLossOnAssetExchangeTransactions0.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:IncreaseDecreaseInContractWithCustomerRefundLiability

ccoi:IncreaseDecreaseInContractWithCustomerRefundLiability


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value-615000.0474000.0-245000.0-231000.0-303000.0-94000.0599000.02053000.0-452000.0-3331000.0-28000.0244000.0
Percentage of IncreaseDecreaseInContractWithCustomerRefundLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:InterestAndOtherIncomeExpense

ccoi:InterestAndOtherIncomeExpense


Interest
Period End2021-06-302021-03-312020-06-302020-03-31
Value64000.0744000.0735000.0-699000.0
Percentage of InterestAndOtherIncomeExpense100.0100.0100.0100.0

ccoi:LossOnAmendmentOfFinanceLeases

ccoi:LossOnAmendmentOfFinanceLeases


Loss
Period End2020-09-30
Value505000.0
Percentage of LossOnAmendmentOfFinanceLeases100.0

ccoi:OperatingLeaseFixedAnnualRent us-gaap:RelatedPartyTransaction, us-gaap:RelatedPartyTransactionsByRelatedParty

ccoi:OperatingLeaseFixedAnnualRent

us-gaap:LeaseAgreements, srt:ChiefExecutiveOfficer


Operating
Period End2021-06-302021-03-312020-12-31
Value01000000.00
Percentage of OperatingLeaseFixedAnnualRent0.0100.00.0

ccoi:PropertyPlantAndEquipmentCompensationCostsCapitalized

ccoi:PropertyPlantAndEquipmentCompensationCostsCapitalized


Property
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-31
Value4.23.23.03.02.92.72.72.62.62.72.62.52.42.42.12.22.62.22.02.12.12.21.72.01.92.01.81.81.81.92.01.81.71.71.71.81.71.9
Percentage of PropertyPlantAndEquipmentCompensationCostsCapitalized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ccoi:RedemptionPricePer1000AggregatePrincipalAmount us-gaap:LongtermDebtType

ccoi:RedemptionPricePer1000AggregatePrincipalAmount

ccoi:SeniorSecuredNotesDue2022


Redemption
Period End2021-04-06
Value41.415
Percentage of RedemptionPricePer1000AggregatePrincipalAmount100.0

ccoi:RedemptionPricePer1000AggregatePrincipalAmount us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:SecuredDebt, us-gaap:SubsequentEvent


Redemption
Period End2021-04-06
Value41.415
Percentage of RedemptionPricePer1000AggregatePrincipalAmount100.0

ccoi:RedemptionValue us-gaap:LongtermDebtType

ccoi:RedemptionValue

ccoi:SeniorSecuredNotesDue2022


Redemption
Period End2021-04-06
Value1900000.0
Percentage of RedemptionValue100.0

ccoi:SpeedPerSecondToBandwidthIntensiveUsers us-gaap:Range

ccoi:SpeedPerSecondToBandwidthIntensiveUsers

srt:Maximum


Speed
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value0100.0000100.000
Percentage of SpeedPerSecondToBandwidthIntensiveUsers0.0100.00.00.00.0100.00.00.0

srt:Minimum


Speed
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value0100.0000100.000
Percentage of SpeedPerSecondToBandwidthIntensiveUsers0.0100.00.00.00.0100.00.00.0

us-gaap:AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease

us-gaap:AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease


Allowance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-31
Value1187000.02012000.01055000.01174000.01432000.01336000.0
Percentage of AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivableRecoveries

us-gaap:AllowanceForDoubtfulAccountsReceivableRecoveries


Allowance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-31
Value400000.01200000.0400000.0400000.0200000.0200000.0
Percentage of AllowanceForDoubtfulAccountsReceivableRecoveries100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivableWriteOffs

us-gaap:AllowanceForDoubtfulAccountsReceivableWriteOffs


Allowance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-31
Value971000.02476000.01338000.01085000.01293000.01131000.0
Percentage of AllowanceForDoubtfulAccountsReceivableWriteOffs100.0100.0100.0100.0100.0100.0

us-gaap:AmortizationOfDebtDiscountPremium

us-gaap:AmortizationOfDebtDiscountPremium


Amortization
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value453000.0441000.0468000.0496000.0453000.0477000.0479000.0486000.0428000.0414000.0407000.0375000.0381000.0370000.0340000.0332000.0287000.0280000.0226000.0183000.0480000.0216000.0181000.0117000.037000.0-164000.0-293000.0-286000.01140000.01415000.01390000.01503000.01613000.01580000.01553000.0
Percentage of AmortizationOfDebtDiscountPremium100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalLeaseObligationsIncurred

us-gaap:CapitalLeaseObligationsIncurred


Capital
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value9.8826.3361019393.1642.9652.784.9323.634.9764.3397.1193.6164.496.5255.6235.9575.3196.2373.6023.2817.974103.4664.2179.6113.4474.2245.7796.4252.382187.8524.2183.4232.3125.8577.53511163.3554.823
Percentage of CapitalLeaseObligationsIncurred100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalizedContractCostAmortization

us-gaap:CapitalizedContractCostAmortization


Capitalized
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value4.64.64.24.24.24.34.34.4
Percentage of CapitalizedContractCostAmortization100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonStockDividendsPerShareDeclared

us-gaap:CommonStockDividendsPerShareDeclared


Common
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-10-312016-12-312016-08-032016-09-302016-05-042016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-202013-12-312013-09-302013-04-182013-06-302013-02-202013-03-312012-11-052012-12-312012-08-072012-08-312012-09-30
Value0.780.7550.7350.7050.680.660.640.620.60.580.560.540.520.50.480.460.440.420.40.40.380.380.370.370.360.350.340.420.350.310.30.170.390.370.370.140.130.130.120.120.110.110.10.10.1
Percentage of CommonStockDividendsPerShareDeclared100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ContractWithCustomerLiabilityRevenueRecognized

us-gaap:ContractWithCustomerLiabilityRevenueRecognized


Contract
Period End2021-06-302021-03-312020-09-302020-06-302020-03-312019-09-302019-06-302019-03-31
Value1800000.01800000.01600000.01800000.01600000.01700000.01700000.01700000.0
Percentage of ContractWithCustomerLiabilityRevenueRecognized100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ContributionOfProperty

us-gaap:ContributionOfProperty


Contribution
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
Value10000.069000.0205000.036000.0207000.087000.0148000.0536000.092000.0416000.0343000.0117000.0
Percentage of ContributionOfProperty100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentRedemptionPricePercentage us-gaap:LongtermDebtType

us-gaap:DebtInstrumentRedemptionPricePercentage

ccoi:SeniorSecuredNotesDue2022


Debt
Period End2021-03-31
Value103.2
Percentage of DebtInstrumentRedemptionPricePercentage100.0

us-gaap:SecuredDebt


Debt
Period End2021-03-31
Value103.2
Percentage of DebtInstrumentRedemptionPricePercentage100.0

us-gaap:DividendsCommonStockCash

us-gaap:DividendsCommonStockCash


Dividends
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312015-12-112015-09-112015-06-122015-03-262014-12-122014-12-312014-09-192014-09-302014-06-182014-06-302014-03-272014-03-312013-12-202013-09-252013-06-182013-03-152012-12-122012-11-052012-09-122012-09-30
Value373634323130292827262624232216151816141413137.8827.8821818176.5126.15.55.05.04.54.5
Percentage of DividendsCommonStockCash100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DividendsCommonStockCash us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


Dividends
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value3736343231302928272626242322
Percentage of DividendsCommonStockCash100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectOfExchangeRateOnCashAndCashEquivalentsContinuingOperations

us-gaap:EffectOfExchangeRateOnCashAndCashEquivalentsContinuingOperations


Effect
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-31
Value658000.0-1316000.02065000.01560000.01214000.0-1326000.01077000.0-1583000.0459000.0-495000.0-744000.0-245000.0-1900000.0532000.0486000.01415000.01774000.0383000.0-1276000.021000.0-545000.01454000.0-978000.0-351000.0574000.0-2935000.0-1488000.0-1836000.0158000.0-387000.086000.0945000.0-169000.0-735000.0488000.0571000.0-1065000.0541000.0-911000.0-922000.0236000.0883000.0-13000.0
Percentage of EffectOfExchangeRateOnCashAndCashEquivalentsContinuingOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ExciseAndSalesTaxes

us-gaap:ExciseAndSalesTaxes


Excise
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value4.84.54.23.93.33.74.34.03.23.43.23.03.13.22.92.72.72.62.62.42.22.01.71.80.00.10.10.1
Percentage of ExciseAndSalesTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0

us-gaap:ExtinguishmentOfDebtAmount us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:ExtinguishmentOfDebtAmount

us-gaap:SecuredDebt, us-gaap:SubsequentEvent


Extinguishment
Period End2021-05-06
Value45
Percentage of ExtinguishmentOfDebtAmount100.0

us-gaap:FairValueOfAssetsAcquired

us-gaap:FairValueOfAssetsAcquired


Fair
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value0.00.2993.1292.3432.313.4622.0493.4341.3162.6663.3772.5662.451.7031.5673.307-14.354-15.007
Percentage of FairValueOfAssetsAcquired0.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FinanceLeaseInterestExpense

us-gaap:FinanceLeaseInterestExpense


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value4.6855.2265.0984.8044.5174.4734.4794.4144.4154.357
Percentage of FinanceLeaseInterestExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FinanceLeaseInterestPaymentOnLiability

us-gaap:FinanceLeaseInterestPaymentOnLiability


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value5.1114.9934.8794.6364.7084.4418.6631.6633.4853.295
Percentage of FinanceLeaseInterestPaymentOnLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FinanceLeasePrincipalPayments

us-gaap:FinanceLeasePrincipalPayments


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value6.1925.7444.5989.5093.7166.1672.0622.0291.9763.032.1282.0993.7552.304
Percentage of FinanceLeasePrincipalPayments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FinanceLeaseRightOfUseAssetAmortization

us-gaap:FinanceLeaseRightOfUseAssetAmortization


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value6.3786.3466.7336.3824.9734.7624.9724.9634.9174.971
Percentage of FinanceLeaseRightOfUseAssetAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ForeignCurrencyTransactionGainLossRealized

us-gaap:ForeignCurrencyTransactionGainLossRealized


Foreign
Period End2020-12-312020-09-302020-06-30
Value-14000.002547000.0
Percentage of ForeignCurrencyTransactionGainLossRealized100.00.0100.0

us-gaap:ForeignCurrencyTransactionGainLossUnrealized

us-gaap:ForeignCurrencyTransactionGainLossUnrealized


Foreign
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value-5.2818-19.2-17.3-3.42.9-4.06.1
Percentage of ForeignCurrencyTransactionGainLossUnrealized100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:GainLossOnDispositionOfAssets

us-gaap:GainLossOnDispositionOfAssets


Gain
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value0.129-0.3710.626-0.9820.4480.4540.227-0.3530.2530.2310.3820.288-0.0450.4840.4390.7661.4562.1720.550.6444.2942.1861.8481.1810.8151.0222.6022.8212.7012.2580.9770.1470.012-0.1350.7730.166-0.1540.186
Percentage of GainLossOnDispositionOfAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:GainLossOnRepurchaseOfDebtInstrument us-gaap:LongtermDebtType

us-gaap:GainLossOnRepurchaseOfDebtInstrument

ccoi:SeniorSecuredNotesDue2022


Gain
Period End2021-03-31
Value3.9
Percentage of GainLossOnRepurchaseOfDebtInstrument100.0

us-gaap:SecuredDebt


Gain
Period End2021-03-31
Value3.9
Percentage of GainLossOnRepurchaseOfDebtInstrument100.0

us-gaap:GainLossOnRepurchaseOfDebtInstrument us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

ccoi:SeniorSecuredNotesDue2022, us-gaap:SubsequentEvent


Gain
Period End2021-12-01
Value10
Percentage of GainLossOnRepurchaseOfDebtInstrument0.0

us-gaap:GainLossOnSaleOfPropertyPlantEquipment

us-gaap:GainLossOnSaleOfPropertyPlantEquipment


Gain
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value0.00.0180.0090.0990.2050.0390.2510.0870.1850.5360.0920.4160.3570.1170.3190.3971.0232.1242.0230.6874.4391.9462.0231.1520.7191.5482.813.1142.7312.295
Percentage of GainLossOnSaleOfPropertyPlantEquipment0.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOperatingLiabilities

us-gaap:IncreaseDecreaseInOperatingLiabilities


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value0.8532.951-0.501-4.3060.4561.0673.692-3.7387.866-2.7785.377-3.055-0.413-2.005-1.160.673-0.424-1.665.769-4.2660.3868.379-3.410.077-1.3992.088-0.119-3.2069.288-1.46610-8.1253.3330.3146.604-3.4772.453-1.209
Percentage of IncreaseDecreaseInOperatingLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets

us-gaap:IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets


Increase
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value130000.0-2826000.0-482000.0788000.0-628000.03093000.0-1132000.01315000.0360000.03187000.0-225000.032000.0-582000.01213000.0-501000.0-1845000.0133000.01067000.0-333000.0-179000.01218000.02217000.0-356000.0130000.0-1426000.04550000.0-552000.0-788000.0-1465000.05143000.0875000.0-1926000.01969000.02724000.0-532000.0-838000.0-377000.01288000.0
Percentage of IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestAndOtherIncome

us-gaap:InterestAndOtherIncome


Interest
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value0.5480.4840.7352.205-2.0578.3471.7531.8272.0631.9370.1891.6940.1651.6321.0150.8540.3440.2070.3350.1330.390.050.4170.097-0.0080.140.2680.1371.0930.2920.5890.6580.9250.3970.1480.3750.2380.0810.298
Percentage of InterestAndOtherIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LeaseCost

us-gaap:LeaseCost


Lease
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value15151615131216111212
Percentage of LeaseCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingLeaseCost

us-gaap:OperatingLeaseCost


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value4.6714.4174.5024.2694.4054.1877.2451.6623.4863.295
Percentage of OperatingLeaseCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingLeasePayments

us-gaap:OperatingLeasePayments


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value4.7155.3964.9715.1654.2054.785.0024.134.3334.494
Percentage of OperatingLeasePayments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value1.776-5.216.1925.4082.913-3.4933.35-4.7091.786-1.825-2.256-0.485-6.1982.6111.3123.796.1631.328-5.2950.688-1.9674.074-2.7460.2281.683-7.396-3.058-5.034-0.044-0.4620.5952.3410.326-1.7931.1931.501-3.0681.623
Percentage of OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent us-gaap:StatementEquityComponents

us-gaap:AccumulatedTranslationAdjustment


Other
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value1.776-5.216.1925.4082.913-3.4933.35-4.7091.786-1.825-2.256-0.485-6.1982.611
Percentage of OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromIssuanceOfUnsecuredDebt

us-gaap:ProceedsFromIssuanceOfUnsecuredDebt


Proceeds
Period End2020-12-312020-09-302019-12-312019-09-302019-06-30
Value0.00.00.0060.0152
Percentage of ProceedsFromIssuanceOfUnsecuredDebt0.00.0100.00.0100.0

us-gaap:ProceedsFromRepaymentsOfNotesPayable

us-gaap:ProceedsFromRepaymentsOfNotesPayable


Proceeds
Period End2021-03-312020-12-31
Value-119680000.00
Percentage of ProceedsFromRepaymentsOfNotesPayable100.00.0

us-gaap:ProceedsFromStockOptionsExercised

us-gaap:ProceedsFromStockOptionsExercised


Proceeds
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-30
Value660000.0215000.0207000.0186000.0271000.0718000.0367000.0351000.0746000.0173000.0248000.0518000.0705000.0297000.0303000.0433000.0186000.0300000.0326000.0264000.0424000.0206000.0135000.069000.089000.0130000.095000.0137000.0146000.0155000.0244000.0237000.0522000.0215000.074000.0172000.064000.094000.0262000.0216000.088000.067000.0145000.052000.0
Percentage of ProceedsFromStockOptionsExercised100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProvisionForDoubtfulAccounts

us-gaap:ProvisionForDoubtfulAccounts


Provision
Period End2021-06-302021-03-312020-09-302020-06-302020-03-31
Value800000.0800000.0800000.01300000.01100000.0
Percentage of ProvisionForDoubtfulAccounts100.0100.0100.0100.0100.0

us-gaap:RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty us-gaap:RelatedPartyTransaction, us-gaap:RelatedPartyTransactionsByRelatedParty

us-gaap:RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty

us-gaap:LeaseAgreements, srt:ChiefExecutiveOfficer


Related
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value500000.0400000.0400000.0500000.0500000.0400000.0500000.0300000.0500000.0300000.0400000.0500000.0500000.0
Percentage of RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RepaymentsOfSeniorDebt us-gaap:LongtermDebtType

us-gaap:RepaymentsOfSeniorDebt

ccoi:SeniorSecuredNotesDue2022


Repayments
Period End2021-05-31
Value45
Percentage of RepaymentsOfSeniorDebt100.0

us-gaap:RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability

us-gaap:RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability


Right
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value9.8826.3361019393.1642.9652.784.9323.63
Percentage of RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability

us-gaap:RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability


Right
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value9.8112.72104.172155.532.8425.4551.1410.316
Percentage of RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StockIssuedDuringPeriodSharesShareBasedCompensation us-gaap:TitleOfIndividual

us-gaap:StockIssuedDuringPeriodSharesShareBasedCompensation

ccoi:ExecutiveEmployeesAndDirectors


Stock
Period End2021-03-312020-06-302020-03-31
Value3237000.135280.31975
Percentage of StockIssuedDuringPeriodSharesShareBasedCompensation100.0100.0100.0

us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation us-gaap:TitleOfIndividual

us-gaap:StockIssuedDuringPeriodValueShareBasedCompensation

ccoi:ExecutiveEmployeesAndDirectors


Stock
Period End2021-03-312020-06-302020-03-31
Value191023
Percentage of StockIssuedDuringPeriodValueShareBasedCompensation100.0100.0100.0

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value660000.0215000.0208000.0185000.0270000.0719000.0367000.0351000.0745000.0173000.0248000.0518000.0704000.0297000.0
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value660000.0215000.0208000.0185000.0270000.0719000.0368000.0351000.0745000.0173000.0248000.0518000.0704000.0297000.0
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised100.0100.0100.0100.0100.0100.0100.3100.0100.0100.0100.0100.0100.0100.0

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue


Stock
Period End2020-12-312020-09-30
Value4.2260.269
Percentage of StockRepurchasedAndRetiredDuringPeriodValue100.0100.0

us-gaap:StockRepurchasedAndRetiredDuringPeriodValue us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital


Stock
Period End2020-12-312020-09-30
Value4.2260.269
Percentage of StockRepurchasedAndRetiredDuringPeriodValue100.0100.0

us-gaap:StockRepurchasedDuringPeriodValue

us-gaap:StockRepurchasedDuringPeriodValue


Stock
Period End2020-12-312020-10-012020-09-302017-12-312017-09-302017-06-302016-12-312016-09-302015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value4.23.10.30.00.01.8-1.69999551.70.012198.119101517140.00.00.00.00.01.30.0
Percentage of StockRepurchasedDuringPeriodValue100.0100.0100.00.00.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.00.0100.00.0

ccoi:AccruedInterestPer1000AggregatePrincipalAmount us-gaap:LongtermDebtType

ccoi:AccruedInterestPer1000AggregatePrincipalAmount

ccoi:SeniorSecuredNotesDue2022


Accrued
Period End2021-04-06
Value9.7049
Percentage of AccruedInterestPer1000AggregatePrincipalAmount100.0

ccoi:AccruedInterestPer1000AggregatePrincipalAmount us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:SecuredDebt, us-gaap:SubsequentEvent


Accrued
Period End2021-04-06
Value9.7049
Percentage of AccruedInterestPer1000AggregatePrincipalAmount100.0

ccoi:DeferredTaxAssetsOperatingLeases

ccoi:DeferredTaxAssetsOperatingLeases


Deferred
Period End2020-12-312019-12-31
Value4032
Percentage of DeferredTaxAssetsOperatingLeases100.0100.0

ccoi:DeferredTaxLiabilitiesRightOfUseAssets

ccoi:DeferredTaxLiabilitiesRightOfUseAssets


Deferred
Period End2020-12-312019-12-31
Value3729
Percentage of DeferredTaxLiabilitiesRightOfUseAssets100.0100.0

ccoi:FinanceLeaseLiabilityPaymentsDueAdditional

ccoi:FinanceLeaseLiabilityPaymentsDueAdditional


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value29252120
Percentage of FinanceLeaseLiabilityPaymentsDueAdditional100.0100.0100.0100.0

ccoi:FixedChargeCoverageRatio us-gaap:DebtInstrument, us-gaap:LongtermDebtType

ccoi:FixedChargeCoverageRatio

ccoi:RestrictionOnCertainPayments, ccoi:SeniorSecuredNotesDue2026


Fixed
Period End2021-06-30
Value1.0
Percentage of FixedChargeCoverageRatio100.0

ccoi:FixedChargeCoverageRatio us-gaap:Range, us-gaap:DebtInstrument

srt:Maximum, ccoi:RestrictionOnCertainPayments


Fixed
Period End2021-06-30
Value2.0
Percentage of FixedChargeCoverageRatio200.0

ccoi:FixedChargeCoverageRatio us-gaap:Range, us-gaap:DebtInstrument, us-gaap:LongtermDebtType

srt:Maximum, ccoi:RestrictionOnCertainPayments, ccoi:SeniorSecuredNotesDue2026


Fixed
Period End2021-06-30
Value1.0
Percentage of FixedChargeCoverageRatio100.0

srt:Maximum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorSecuredNotesDue2026


Fixed
Period End2021-06-30
Value1.0
Percentage of FixedChargeCoverageRatio100.0

srt:Minimum, ccoi:RestrictionOnCertainPayments, ccoi:SeniorSecuredNotesDue2026


Fixed
Period End2021-06-30
Value2.0
Percentage of FixedChargeCoverageRatio200.0

srt:Minimum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorSecuredNotesDue2026


Fixed
Period End2021-06-30
Value2.0
Percentage of FixedChargeCoverageRatio200.0

ccoi:LeaseRightOfUseAsset

ccoi:LeaseRightOfUseAsset


Lease
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-31
Value105979990877573
Percentage of LeaseRightOfUseAsset100.0100.0100.0100.0100.0100.0100.0

ccoi:OperatingLossCarryforwardsNotSubjectToExpiration us-gaap:StatementGeographical

ccoi:OperatingLossCarryforwardsNotSubjectToExpiration

srt:Europe


Operating
Period End2020-12-312019-12-31
Value870744
Percentage of OperatingLossCarryforwardsNotSubjectToExpiration100.0100.0

us-gaap:ForeignCountry


Operating
Period End2020-12-312019-12-31
Value1000896
Percentage of OperatingLossCarryforwardsNotSubjectToExpiration114.9120.4

ccoi:RatioOfAdditionalIndebtednessToNetCapital us-gaap:Range, us-gaap:DebtInstrument, us-gaap:LongtermDebtType

ccoi:RatioOfAdditionalIndebtednessToNetCapital

srt:Maximum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorSecuredNotesDue2026


Ratio
Period End2021-06-30
Value1.0
Percentage of RatioOfAdditionalIndebtednessToNetCapital100.0

srt:Maximum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorUnsecuredNotesOf4.375Due2024


Ratio
Period End2021-06-30
Value1.0
Percentage of RatioOfAdditionalIndebtednessToNetCapital100.0

srt:Minimum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SecuredDebt2022NotesAnd2021Notes


Ratio
Period End2021-03-312020-12-312020-09-302020-06-302020-03-312019-09-302019-06-30
Value3.54.254.254.253.53.53.5
Percentage of RatioOfAdditionalIndebtednessToNetCapital0.00.00.00.00.00.00.0

srt:Minimum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorSecuredNotesDue2026


Ratio
Period End2021-06-30
Value4.0
Percentage of RatioOfAdditionalIndebtednessToNetCapital400.0

srt:Minimum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorUnsecuredNotesOf4.375Due2024


Ratio
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-31
Value4.254.04.04.03.54.0
Percentage of RatioOfAdditionalIndebtednessToNetCapital425.00.00.00.00.00.0

srt:Minimum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, us-gaap:SecuredDebt


Ratio
Period End2021-03-312020-12-312020-09-302020-06-30
Value4.253.53.54.0
Percentage of RatioOfAdditionalIndebtednessToNetCapital0.00.00.00.0

ccoi:RedemptionForDebtNoticeIssued us-gaap:LongtermDebtType

ccoi:RedemptionForDebtNoticeIssued

ccoi:SeniorSecuredNotesDue2022


Redemption
Period End2021-04-06
Value45
Percentage of RedemptionForDebtNoticeIssued100.0

ccoi:RedemptionForDebtNoticeIssued us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:SecuredDebt, us-gaap:SubsequentEvent


Redemption
Period End2021-04-06
Value45
Percentage of RedemptionForDebtNoticeIssued100.0

ccoi:UnamortizedDebtIssuanceExpenseCurrent us-gaap:LongtermDebtType

ccoi:UnamortizedDebtIssuanceExpenseCurrent

us-gaap:SecuredDebt


Unamortized
Period End2021-03-31
Value733000.0
Percentage of UnamortizedDebtIssuanceExpenseCurrent100.0

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent

us-gaap:AccrualForTaxesOtherThanIncomeTaxesCurrent


Accrual
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value5918000.06053000.04212000.02360000.04037000.03347000.01359000.01128000.0692000.01210000.01448000.0
Percentage of AccrualForTaxesOtherThanIncomeTaxesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax


Accumulated
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-06-302013-03-312012-12-31
Value-4740000.0-6516000.0-1306000.0-7498000.0-12906000.0-15819000.0-12326000.0-15676000.0-10967000.0-12753000.0-10928000.0-8672000.0-8187000.0-1989000.0-4600000.0-5912000.0-9702000.0-15865000.0-17193000.0-11898000.0-12586000.0-10619000.0-14693000.0-11947000.0-12175000.0-13858000.0-6462000.0-3404000.01630000.02136000.01541000.0-800000.0-1126000.0667000.0
Percentage of AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForDoubtfulAccountsReceivableCurrent

us-gaap:AllowanceForDoubtfulAccountsReceivableCurrent


Allowance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value1673000.01457000.01921000.02204000.02115000.01976000.01771000.01758000.01782000.01353000.01263000.01614000.01131000.01110000.01499000.02044000.01731000.01543000.01734000.01804000.01102000.01241000.01757000.01589000.01872000.01902000.01707000.02012000.01817000.02192000.01871000.01905000.01879000.01759000.03083000.02822000.02914000.03027000.03345000.02593000.02602000.02464000.0
Percentage of AllowanceForDoubtfulAccountsReceivableCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDue

us-gaap:CapitalLeasesFutureMinimumPaymentsDue


Capital
Period End2020-12-31
Value39
Percentage of CapitalLeasesFutureMinimumPaymentsDue100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDueCurrent

us-gaap:CapitalLeasesFutureMinimumPaymentsDueCurrent


Capital
Period End2020-12-31
Value19
Percentage of CapitalLeasesFutureMinimumPaymentsDueCurrent100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInFiveYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInFiveYears


Capital
Period End2020-12-31
Value1240000.0
Percentage of CapitalLeasesFutureMinimumPaymentsDueInFiveYears100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInFourYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInFourYears


Capital
Period End2020-12-31
Value3119000.0
Percentage of CapitalLeasesFutureMinimumPaymentsDueInFourYears100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInThreeYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInThreeYears


Capital
Period End2020-12-31
Value5586000.0
Percentage of CapitalLeasesFutureMinimumPaymentsDueInThreeYears100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInTwoYears

us-gaap:CapitalLeasesFutureMinimumPaymentsDueInTwoYears


Capital
Period End2020-12-31
Value8531000.0
Percentage of CapitalLeasesFutureMinimumPaymentsDueInTwoYears100.0

us-gaap:CapitalLeasesFutureMinimumPaymentsDueThereafter

us-gaap:CapitalLeasesFutureMinimumPaymentsDueThereafter


Capital
Period End2020-12-31
Value1690000.0
Percentage of CapitalLeasesFutureMinimumPaymentsDueThereafter100.0

us-gaap:CapitalizedContractCostNet

us-gaap:CapitalizedContractCostNet


Capitalized
Period End2020-12-312019-12-312018-12-31
Value201818
Percentage of CapitalizedContractCostNet100.0100.0100.0

us-gaap:ContractualObligation us-gaap:LongtermDebtType, us-gaap:PropertyPlantAndEquipmentByType

us-gaap:ContractualObligation

us-gaap:NotesPayableOtherPayables, us-gaap:Equipment


Contractual
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-31
Value3.45.37.71012121212111211121211105.5
Percentage of ContractualObligation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentCarryingAmount us-gaap:LongtermDebtType

us-gaap:DebtInstrumentCarryingAmount

ccoi:SeniorSecuredNotesDue2022


Debt
Period End2021-05-06
Value284
Percentage of DebtInstrumentCarryingAmount100.0

ccoi:SeniorSecuredNotesDue2026


Debt
Period End2021-06-30
Value500
Percentage of DebtInstrumentCarryingAmount0.0

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-25
Value350350350350350135135135135
Percentage of DebtInstrumentCarryingAmount0.00.00.00.00.00.00.00.00.0

us-gaap:SecuredDebt


Debt
Period End2021-03-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-07-312018-06-302018-03-312017-12-312017-09-30
Value329445445445189445445445445445375375375375375
Percentage of DebtInstrumentCarryingAmount0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:UnsecuredDebt


Debt
Period End2020-12-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value445445189445189189189189189189189189189
Percentage of DebtInstrumentCarryingAmount0.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:DebtInstrumentCarryingAmount us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

us-gaap:SecuredDebt, us-gaap:SubsequentEvent


Debt
Period End2021-05-06
Value284
Percentage of DebtInstrumentCarryingAmount100.0

us-gaap:DebtInstrumentFaceAmount us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:LongtermDebtType

us-gaap:DebtInstrumentFaceAmount

us-gaap:FairValueInputsLevel2, ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2020-09-30
Value410
Percentage of DebtInstrumentFaceAmount100.0

us-gaap:DebtInstrumentFaceAmount us-gaap:LongtermDebtType

ccoi:SeniorSecuredNotesDue2022


Debt
Period End2021-06-302021-03-31
Value284115
Percentage of DebtInstrumentFaceAmount0.00.0

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2021-06-302020-09-302020-06-302020-06-032019-06-302019-06-25
Value350350215215135135
Percentage of DebtInstrumentFaceAmount0.085.30.00.00.00.0

us-gaap:SecuredDebt


Debt
Period End2021-03-312020-09-302020-06-302019-06-302018-08-312016-12-312015-02-28
Value11544535013570125250
Percentage of DebtInstrumentFaceAmount0.0108.40.00.00.00.00.0

us-gaap:DebtInstrumentFairValue us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:LongtermDebtType

us-gaap:DebtInstrumentFairValue

us-gaap:FairValueInputsLevel2, ccoi:SeniorSecuredNotesDue2026


Debt
Period End2021-06-30
Value510
Percentage of DebtInstrumentFairValue100.0

us-gaap:FairValueInputsLevel2, ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value424419437416393151155149
Percentage of DebtInstrumentFairValue83.20.00.00.00.00.00.00.0

us-gaap:FairValueInputsLevel2, us-gaap:SecuredDebt


Debt
Period End2021-03-312020-09-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302015-09-302015-06-30
Value337455447191461461457438449383383392396245247
Percentage of DebtInstrumentFairValue0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:FairValueInputsLevel2, us-gaap:UnsecuredDebt


Debt
Period End2020-12-312020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302015-09-302015-06-30
Value458456187466191191191188190190191193194191190
Percentage of DebtInstrumentFairValue0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:DebtInstrumentUnamortizedDiscount

us-gaap:DebtInstrumentUnamortizedDiscount


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value0.0410.080.1360.2450.2910.3130.350.3910.3960.4360.3950.3371.4143.0994.756.3657.9479.49411121315161820
Percentage of DebtInstrumentUnamortizedDiscount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtInstrumentUnamortizedDiscount us-gaap:LongtermDebtType, us-gaap:PropertyPlantAndEquipmentByType

us-gaap:NotesPayableOtherPayables, us-gaap:Equipment


Debt
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-31
Value0.0410.10.10.30.30.30.40.40.40.50.40.50.50.40.40.3
Percentage of DebtInstrumentUnamortizedDiscount100.0125.073.5122.4103.195.8114.3102.3101.0114.7101.30.00.00.0118.70.0

us-gaap:DebtInstrumentUnamortizedPremium us-gaap:LongtermDebtType

us-gaap:DebtInstrumentUnamortizedPremium

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2020-12-312020-09-302020-06-302019-12-31
Value1142000.01164000.01183000.00
Percentage of DebtInstrumentUnamortizedPremium100.0100.0100.00.0

us-gaap:SecuredDebt


Debt
Period End2020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302016-12-31
Value544000.0656000.0767000.0877000.0985000.01092000.01197000.01302000.01405000.01507000.0340000.0360000.0382000.0402000.0462000.0
Percentage of DebtInstrumentUnamortizedPremium47.656.464.80.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:DebtInstrumentUnamortizedPremiumCurrent us-gaap:LongtermDebtType

us-gaap:DebtInstrumentUnamortizedPremiumCurrent

us-gaap:SecuredDebt


Debt
Period End2021-03-31
Value430000.0
Percentage of DebtInstrumentUnamortizedPremiumCurrent100.0

us-gaap:DebtInstrumentUnamortizedPremiumNoncurrent us-gaap:LongtermDebtType

us-gaap:DebtInstrumentUnamortizedPremiumNoncurrent

ccoi:SeniorSecuredNotesDue2026


Debt
Period End2021-06-30
Value1698000.0
Percentage of DebtInstrumentUnamortizedPremiumNoncurrent100.0

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Debt
Period End2021-06-302021-03-312020-12-31
Value959000.01020000.01142000.0
Percentage of DebtInstrumentUnamortizedPremiumNoncurrent56.50.00.0

us-gaap:DeferredIncomeTaxLiabilities

us-gaap:DeferredIncomeTaxLiabilities


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312013-12-312012-12-312011-12-31
Value1801721311291251151.3984.0155.62
Percentage of DeferredIncomeTaxLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredRevenueCurrent

us-gaap:DeferredRevenueCurrent


Deferred
Period End2020-12-312019-12-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value4651000.04316000.04504000.04280000.04374000.04475000.04758000.04334000.04303000.04307000.04174000.04132000.03978000.03893000.0
Percentage of DeferredRevenueCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsGross

us-gaap:DeferredTaxAssetsGross


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value320293261276378374398412358352
Percentage of DeferredTaxAssetsGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards

us-gaap:DeferredTaxAssetsOperatingLossCarryforwards


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value273255255271373370366402345335340
Percentage of DeferredTaxAssetsOperatingLossCarryforwards100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsTaxCreditCarryforwards

us-gaap:DeferredTaxAssetsTaxCreditCarryforwards


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value1965000.02261000.02458000.02771000.02237000.02317000.02208000.02775000.02758000.02437000.02748000.0
Percentage of DeferredTaxAssetsTaxCreditCarryforwards100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost

us-gaap:DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312011-12-312010-12-31
Value4901000.04116000.03322000.02327000.02279000.01474000.0849000.0566000.0705000.0
Percentage of DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxLiabilitiesDeferredExpenseReservesAndAccruals

us-gaap:DeferredTaxLiabilitiesDeferredExpenseReservesAndAccruals


Deferred
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-31
Value1051071011069597
Percentage of DeferredTaxLiabilitiesDeferredExpenseReservesAndAccruals100.0100.0100.0100.0100.0100.0

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
Value373429222918-7.857-6.685
Percentage of DeferredTaxLiabilitiesPropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DepositsAssetsNoncurrent

us-gaap:DepositsAssetsNoncurrent


Deposits
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value15131413131313131414115.572
Percentage of DepositsAssetsNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EmployeeRelatedLiabilitiesCurrent

us-gaap:EmployeeRelatedLiabilitiesCurrent


Employee
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value8024000.06613000.07695000.05139000.04170000.03455000.03371000.02952000.02358000.02160000.02155000.0
Percentage of EmployeeRelatedLiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized


Employee
Period End2020-12-31
Value40
Percentage of EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized100.0

us-gaap:FinanceLeaseLiability

us-gaap:FinanceLeaseLiability


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value224218219212
Percentage of FinanceLeaseLiability100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityCurrent

us-gaap:FinanceLeaseLiabilityCurrent


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value16151515148.2688.1547.8847.77.2937.074
Percentage of FinanceLeaseLiabilityCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityNoncurrent

us-gaap:FinanceLeaseLiabilityNoncurrent


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value208202203197189159161160160157156
Percentage of FinanceLeaseLiabilityNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDue

us-gaap:FinanceLeaseLiabilityPaymentsDue


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value394387392383
Percentage of FinanceLeaseLiabilityPaymentsDue100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDueInNextRollingTwelveMonths

us-gaap:FinanceLeaseLiabilityPaymentsDueInNextRollingTwelveMonths


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value34343433
Percentage of FinanceLeaseLiabilityPaymentsDueInNextRollingTwelveMonths100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingAfterYearFive

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingAfterYearFive


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value235229232225
Percentage of FinanceLeaseLiabilityPaymentsDueInRollingAfterYearFive100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearFive

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearFive


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value25252728
Percentage of FinanceLeaseLiabilityPaymentsDueInRollingYearFive100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearFour

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearFour


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value32323231
Percentage of FinanceLeaseLiabilityPaymentsDueInRollingYearFour100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearThree

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearThree


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value32323231
Percentage of FinanceLeaseLiabilityPaymentsDueInRollingYearThree100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearTwo

us-gaap:FinanceLeaseLiabilityPaymentsDueInRollingYearTwo


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value33333332
Percentage of FinanceLeaseLiabilityPaymentsDueInRollingYearTwo100.0100.0100.0100.0

us-gaap:FinanceLeaseLiabilityUndiscountedExcessAmount

us-gaap:FinanceLeaseLiabilityUndiscountedExcessAmount


Finance
Period End2021-06-302021-03-312020-12-312020-09-30
Value169169172170
Percentage of FinanceLeaseLiabilityUndiscountedExcessAmount100.0100.0100.0100.0

us-gaap:FinanceLeaseWeightedAverageDiscountRatePercent

us-gaap:FinanceLeaseWeightedAverageDiscountRatePercent


Finance
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value9.810.110.310.50.1080.10911.010.50.1060.107
Percentage of FinanceLeaseWeightedAverageDiscountRatePercent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestPayableCurrent

us-gaap:InterestPayableCurrent


Interest
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-31
Value8.268101110107.7811111117.3923.543
Percentage of InterestPayableCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestPayableCurrent us-gaap:LongtermDebtType

ccoi:SeniorSecuredNotesDue2022


Interest
Period End2021-03-31
Value0.4
Percentage of InterestPayableCurrent0.0

us-gaap:SecuredDebt


Interest
Period End2021-03-31
Value0.4
Percentage of InterestPayableCurrent0.0

us-gaap:InterestPayableCurrent us-gaap:LongtermDebtType, us-gaap:SubsequentEventType

ccoi:SeniorSecuredNotesDue2022, us-gaap:SubsequentEvent


Interest
Period End2021-12-01
Value11
Percentage of InterestPayableCurrent0.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive


Lessee
Period End2021-03-312020-12-312020-09-30
Value114118103
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive100.0100.0100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive


Lessee
Period End2021-03-312020-12-312020-09-30
Value121212
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive100.0100.0100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour


Lessee
Period End2021-03-312020-12-312020-09-30
Value141514
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour100.0100.0100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree


Lessee
Period End2021-03-312020-12-312020-09-30
Value161615
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree100.0100.0100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo


Lessee
Period End2021-03-312020-12-312020-09-30
Value161616
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo100.0100.0100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths


Lessee
Period End2021-03-312020-12-312020-09-30
Value171717
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths100.0100.0100.0

us-gaap:LongTermDebtFairValue us-gaap:LongtermDebtType

us-gaap:LongTermDebtFairValue

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Long
Period End2020-12-312019-12-31
Value429151
Percentage of LongTermDebtFairValue100.0100.0

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths


Long
Period End2020-12-31
Value6922000.0
Percentage of LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths100.0

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour


Long
Period End2020-12-31
Value429
Percentage of LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour100.0

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo

us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo


Long
Period End2020-12-31
Value445
Percentage of LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo100.0

us-gaap:LossContingencyRangeOfPossibleLossPortionNotAccrued

us-gaap:LossContingencyRangeOfPossibleLossPortionNotAccrued


Loss
Period End2021-06-302021-03-312020-12-312020-09-30
Value3500000.03400000.03300000.03300000.0
Percentage of LossContingencyRangeOfPossibleLossPortionNotAccrued100.0100.0100.0100.0

us-gaap:OperatingLeaseWeightedAverageDiscountRatePercent

us-gaap:OperatingLeaseWeightedAverageDiscountRatePercent


Operating
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value5.55.65.65.40.0540.0565.65.70.0570.056
Percentage of OperatingLeaseWeightedAverageDiscountRatePercent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingLossCarryforwards

us-gaap:OperatingLossCarryforwards


Operating
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value110099410001000120012001200130011001100
Percentage of OperatingLossCarryforwards100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingLossCarryforwards us-gaap:StatementGeographical

country:MX


Operating
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value5.33.34.05.31.11.71.81.8
Percentage of OperatingLossCarryforwards0.50.30.40.50.10.10.10.1

country:US


Operating
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-31
Value6097131150465446390395
Percentage of OperatingLossCarryforwards5.59.813.115.138.837.232.530.4

srt:Europe


Operating
Period End2020-12-312019-12-31
Value1000890
Percentage of OperatingLossCarryforwards90.989.5

us-gaap:PropertyPlantAndEquipmentFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:NonmonetaryTransactionType, us-gaap:PropertyPlantAndEquipmentByType

us-gaap:PropertyPlantAndEquipmentFairValueDisclosure

us-gaap:FairValueInputsLevel3, us-gaap:ExchangeOfProductiveAssets, us-gaap:Equipment


Property
Period End2020-12-312019-12-312019-03-312018-12-312018-03-312017-12-31
Value1.13.31.73.20.49.1
Percentage of PropertyPlantAndEquipmentFairValueDisclosure100.0100.0100.0100.0100.0100.0

us-gaap:RatioOfIndebtednessToNetCapital1 us-gaap:Range, us-gaap:DebtInstrument, us-gaap:LongtermDebtType

us-gaap:RatioOfIndebtednessToNetCapital1

srt:Maximum, ccoi:RestrictionOnCertainPayments, ccoi:SeniorSecuredNotesDue2026


Ratio
Period End2021-06-30
Value1.0
Percentage of RatioOfIndebtednessToNetCapital1100.0

srt:Maximum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorSecuredNotesDue2026


Ratio
Period End2021-06-30
Value1.0
Percentage of RatioOfIndebtednessToNetCapital1100.0

srt:Maximum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorUnsecuredNotesOf4.375Due2024


Ratio
Period End2021-06-30
Value1.0
Percentage of RatioOfIndebtednessToNetCapital1100.0

srt:Minimum, ccoi:RestrictionOnCertainPayments, ccoi:SeniorSecuredNotesDue2026


Ratio
Period End2021-06-30
Value6.0
Percentage of RatioOfIndebtednessToNetCapital1600.0

srt:Minimum, ccoi:RestrictionOnIncurringAdditionalIndebtedness, ccoi:SeniorSecuredNotesDue2026


Ratio
Period End2021-06-30
Value6.0
Percentage of RatioOfIndebtednessToNetCapital1600.0

us-gaap:SecuredDebtCurrent

us-gaap:SecuredDebtCurrent


Secured
Period End2021-03-31
Value328
Percentage of SecuredDebtCurrent100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue

us-gaap:RestrictedStock


Share
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-31
Value55.745.441.1238.1135.9432.2528.2618.6916.1211.34
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice

us-gaap:EmployeeStockOption


Share
Period End2020-12-31
Value47.63
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue

us-gaap:EmployeeStockOption


Share
Period End2020-12-31
Value1700000.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue

us-gaap:EmployeeStockOption


Share
Period End2020-12-31
Value1600000.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice

us-gaap:EmployeeStockOption


Share
Period End2020-12-31
Value52.71
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice100.0

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 us-gaap:AwardType

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1

us-gaap:EmployeeStockOption


Sharebased
Period End2020-12-31
Value1500000.0
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1100.0

us-gaap:StockRepurchaseProgramAuthorizedAmount1

us-gaap:StockRepurchaseProgramAuthorizedAmount1


Stock
Period End2020-12-31
Value50
Percentage of StockRepurchaseProgramAuthorizedAmount1100.0

us-gaap:StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1

us-gaap:StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1


Stock
Period End2021-06-302021-03-312020-12-312020-09-30
Value30303034
Percentage of StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1100.0100.0100.0100.0

us-gaap:UnamortizedDebtIssuanceExpense us-gaap:LongtermDebtType

us-gaap:UnamortizedDebtIssuanceExpense

ccoi:SeniorSecuredNotesDue2026


Unamortized
Period End2021-06-30
Value1277000.0
Percentage of UnamortizedDebtIssuanceExpense100.0

ccoi:SeniorUnsecuredNotesOf4.375Due2024


Unamortized
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-30
Value2538000.02751000.02961000.03166000.01480000.01341000.01410000.01483000.0
Percentage of UnamortizedDebtIssuanceExpense198.70.00.00.00.00.00.00.0

us-gaap:SecuredDebt


Unamortized
Period End2021-06-302020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302016-12-31
Value1052000.01052000.01267000.03365000.01690000.01897000.02101000.02301000.02500000.02695000.02887000.01668000.01769000.01870000.01969000.02257000.0
Percentage of UnamortizedDebtIssuanceExpense82.40.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:UnsecuredDebt


Unamortized
Period End2020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302016-12-31
Value857000.0857000.0696000.0857000.01015000.01171000.01325000.01476000.01625000.01772000.01917000.02060000.02200000.02575000.0
Percentage of UnamortizedDebtIssuanceExpense0.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary


Unrecorded
Period End2020-12-31
Value700000.0
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary100.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary


Unrecorded
Period End2020-12-31
Value2500000.0
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary100.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary


Unrecorded
Period End2020-12-31
Value700000.0
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary100.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary


Unrecorded
Period End2020-12-31
Value800000.0
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary100.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary


Unrecorded
Period End2020-12-31
Value700000.0
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary100.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount


Unrecorded
Period End2021-06-302021-03-312020-12-312020-09-302020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value3.3245.0356.7868.2929.3749.1229.0639.0788.6938.6868.28314
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount us-gaap:UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

ccoi:EquipmentAndServices


Unrecorded
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-31
Value107.68.55.05.68.16.62440
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount156.283.9102.633.80.00.00.00.00.0

us-gaap:UseRights


Unrecorded
Period End2020-12-312019-12-312018-12-31
Value212012
Percentage of UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount309.5224.0152.1

us-gaap:UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears

us-gaap:UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears


Unrecorded
Period End2020-12-31
Value15
Percentage of UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears100.0

us-gaap:ValuationAllowancesAndReservesBalance us-gaap:ValuationAllowancesAndReservesType

us-gaap:ValuationAllowancesAndReservesBalance

us-gaap:ValuationAllowanceOfDeferredTaxAssets


Valuation
Period End2020-12-312019-12-312018-12-312017-12-312016-12-312015-12-312014-12-312013-12-312012-12-312011-12-312010-12-312009-12-31
Value150131126129210213345354347337343340
Percentage of ValuationAllowancesAndReservesBalance100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Line plots across dimensions of each concept


us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecurities
(None,)
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amountus-gaap: Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities
TTM Greenblatt ROC
_
(None,)
T T M  Greenblatt  R O C_
us-gaap:AllocatedShareBasedCompensationExpense
us-gaap:IncomeStatementLocation
(None,)
Allocated Share Based Compensation Expenseus-gaap: Income Statement Location
us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax
us-gaap:ProductOrService
(None,)
Revenue From Contract With Customer Including Assessed Taxus-gaap: Product Or Service
us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax
us-gaap:StatementGeographical
(None,)
Revenue From Contract With Customer Including Assessed Taxus-gaap: Statement Geographical
us-gaap:RevenueFromContractWithCustomerIncludingAssessedTax
us-gaap:ProductOrService, us-gaap:StatementGeographical
('ccoi:OnNetServices', None)
Revenue From Contract With Customer Including Assessed Taxus-gaap: Product Or Service, us-gaap: Statement Geographical
us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents
(None,)
Stockholders Equityus-gaap: Statement Equity Components
us-gaap:NoncurrentAssets
us-gaap:StatementGeographical
(None,)
Noncurrent Assetsus-gaap: Statement Geographical
us-gaap:PropertyPlantAndEquipmentGross
us-gaap:FiniteLivedIntangibleAssetsByMajorClass, us-gaap:PropertyPlantAndEquipmentByType
('us-gaap:Assets', None)
Property Plant And Equipment Grossus-gaap: Finite Lived Intangible Assets By Major Class, us-gaap: Property Plant And Equipment By Type
us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents
(None,)
Stockholders Equityus-gaap: Statement Equity Components