RCUS

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

Plots across concepts

IncomeStatement

Balance Sheet

Assets

Current Assets

NonCurrent Assets

PropertyPlantAndEquipmentNet

Liabilities

Current Liabilities

Stockholders Equity

CashFlow

NetCashProvidedByUsedInOperatingActivities

NetCashProvidedByUsedInInvestingActivities

OperatingLeaseLiability

LesseeOperatingLeaseLiabilityPaymentsDue

Tables

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:CommonStockValue	██▆▆▆▁▁▁▁▁▁	0.007	0.007	0.006	0.006	0.006	0.004	0.004	0.004	0.004	0.004	0.004	NA	NA	NA	NA	NA
us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding		NA	NA	63.527932	65.145707	48.556843	44.282607	NA	43.939281	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:WeightedAverageNumberOfSharesOutstandingBasic		NA	NA	63.527932	62.599193	50.15316	45.953213	NA	45.787137	45.409588	44.532073	NA	44.452184	44.450312	11.598421	NA	3.994915
us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted	█▁	69.745297	67.082161	NA	NA	48.556843	44.282607	44.056407	43.939281	43.797718	43.508592	43.163412	42.838098	42.533641	9.488352	2.208065	1.949258
us-gaap:EarningsPerShareBasic		NA	NA	NA	0.03	NA	NA	NA	-0.51	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:EarningsPerShareDiluted		NA	NA	NA	0.03	NA	NA	NA	-0.51	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:EarningsPerShareBasicAndDiluted	▁█	-1.09	-1.08	NA	NA	-0.93	-0.63	-0.3699999999999999	-0.51	-0.64	-0.41	-0.27	-0.25	-0.32	-1.37	-5.560000000000002	-11.86
us-gaap:IncomeLossFromContinuingOperationsPerBasicShare		NA	NA	-8.2e-07	3e-08	-9.300000000000001e-07	-6.3e-07	NA	-5.1e-07	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:IncomeLossFromContinuingOperationsPerDilutedShare		NA	NA	-8.2e-07	3e-08	-9.300000000000001e-07	-6.3e-07	NA	-5.1e-07	NA	NA	NA	NA	NA	NA	NA	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:AllocatedShareBasedCompensationExpense	█▁	13.367	12.761	NA	6.002	4.47	3.462	NA	2.74	2.13	1.674	NA	1.048	1.116	0.656	NA	0.136
us-gaap:ComprehensiveIncomeNetOfTax	▁▁▃█▄▅▆▆▅▆▇▇▇▇▇▆	-76.014	-72.639	-51.89	1.759	-45.218	-27.529	-16.587	-22.411	-28.006	-17.534	-12.294	-10.837	-13.519	-13.009	-13.243	-23.108
us-gaap:GeneralAndAdministrativeExpense	██▆▅▅▃▃▄▃▂▂▂▂▁▁▁	16.826	15.821	12.787	11.177	11.432	7.008	6.591	7.758	5.911	4.969	3.61	3.577	3.45	2.929	2.448	1.862
us-gaap:NetIncomeLoss	▁▁▃█▄▅▆▆▅▆▇▇▇▇▇▆	-75.97	-72.593	-51.853	1.822	-45.074	-27.753	-16.598	-22.352	-28.09	-17.67	-12.295	-10.812	-13.533	-12.954	-13.21	-23.122
us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents us-gaap:RetainedEarnings	▁█	-75.97	-72.593	NA	1.822	-45.074	-27.753	NA	-22.352	-28.09	-17.67	NA	-10.812	-13.533	-12.954	NA	NA
us-gaap:NonoperatingIncomeExpense	▁▁▁▂▂▃▄▄▄▄▄▅█▂▁▁	0.166	0.154	0.159	0.27	0.301	0.647	0.929	0.897	1.07	1.103	1.189	1.333	2.366	0.377	0.134	0.012
us-gaap:OperatingExpenses	██▆▆▄▃▂▂▃▂▁▁▁▁▁▂	85.597	82.208	61.499	62.978	47.125	30.15	27.277	24.999	30.91	20.523	15.046	16.436	17.149	14.581	14.594	23.297
us-gaap:OperatingIncomeLoss	▁▁▃█▄▅▆▆▅▆▇▇▆▇▇▆	-76.136	-72.747	-52.012	1.552	-45.375	-28.4	-17.527	-23.249	-29.16	-18.773	-13.484	-12.145	-15.899	-13.331	-13.344	-23.134
us-gaap:OtherComprehensiveIncomeLossNetOfTax	█▁	-0.044	-0.046	NA	-0.063	-0.144	0.224	NA	-0.06	0.084	0.136	NA	-0.025	0.014	-0.055	NA	NA
us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedOtherComprehensiveIncome	█▁	-0.044	-0.046	NA	-0.063	-0.144	0.224	NA	-0.06	0.084	0.136	NA	-0.025	0.014	-0.055	NA	NA
us-gaap:ProfitLoss	▁▁▃█▄▅▆▆▅▆▇▇▇▇▇	-75.97	-72.593	-51.853	1.822	-45.074	-27.753	-16.598	-22.352	-28.09	-17.67	-12.295	-10.811	-13.534	-12.954	-13.21	NA
us-gaap:ResearchAndDevelopmentExpense	██▆▆▄▂▂▂▃▂▁▁▁▁▁▂	68.771	66.387	48.712	51.801	35.693	23.142	20.686	17.241	24.999	15.554	11.436	12.859	13.699	11.652	12.146	21.435
us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost us-gaap:CounterpartyName,us-gaap:TypeOfArrangement rcus:StrataOncologyInc,rcus:StrataAgreement	▁█	0.5	0.6	NA	0.3	0.6	0.4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost us-gaap:TypeOfArrangement rcus:AstraZenecaAgreement	▄	0.3	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax	▂▂▂█▁▁▂▁▁▁▁▁▁▁▁▁	9.461	9.461	9.487	64.53	1.75	1.75	9.75	1.75	1.75	1.75	1.562	4.291	1.25	1.25	1.25	0.163
us-gaap:Revenues	▂▂▂█▁▁▂▁▁▁▁▁▁▁▁▁	9.461	9.461	9.487	64.53	1.75	1.75	9.75	1.75	1.75	1.75	1.562	4.291	1.25	1.25	1.25	0.163

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:Assets	██▆▇▄▁▁▁▂▂▂▂▂▂▁	898.773	935.119	772.292	811.075	481.389	176.144	203.11	216.957	238.974	258.53	274.925	286.721	293.865	305.399	190.486	NA
us-gaap:Liabilities	█▇▇▇▁▁▁▁▁▁▁▁▁▁▁	294.218	270.329	269.988	266.658	52.679	35.506	39.268	39.73	42.328	36.963	39.983	41.6	39.291	38.808	36.618	NA
us-gaap:LiabilitiesAndStockholdersEquity	██▆▇▄▁▁▁▂▂▂▂▂▂▁	898.773	935.119	772.292	811.075	481.389	176.144	203.11	216.957	238.974	258.53	274.925	286.721	293.865	305.399	190.486	NA
us-gaap:StockholdersEquity	▇█▆▇▆▃▃▃▄▄▄▄▄▄▁	604.555	664.79	502.304	544.417	428.71	140.638	163.842	177.227	196.646	221.567	234.942	245.121	254.574	266.591	-72.328	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:AssetsCurrent	▇█▇█▄▁▁▁▂▂▂▂▂▂▁	745.954	841.87	735.815	797.199	471.599	166.217	192.705	200.488	227.733	245.015	258.948	265.28	267.441	282.068	176.869	NA
us-gaap:CashAndCashEquivalentsAtCarryingValue	▇█▄▅▆▂▂▂▂▂▂▂▄▄▃▁	320.482	390.26	173.415	221.849	285.185	67.326	57.937	78.992	76.068	68.499	71.064	74.889	169.998	198.116	98.426	18.306
us-gaap:PrepaidExpenseAndOtherAssetsCurrent	█▄▂▅▄▃▂▂▂▂▁▁▁▁▁	21.967	8.68	5.471	11.816	8.665	8.007	4.303	4.223	3.273	3.08	2.321	2.329	1.55	1.834	1.141	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:PropertyPlantAndEquipmentGross		NA	NA	25.095	NA	NA	NA	20.551	20.376	19.841	19.622	18.75	18.458	18.235	16.619	15.208	NA
us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType rcus:CapitalizedSoftware		NA	NA	0.225	NA	NA	NA	0.146	0.146	0.146	0.146	0.146	0.146	0.146	0.131	0.131	NA
us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType us-gaap:ConstructionInProgress		NA	NA	2.336	NA	NA	NA	0.238	0.24	0.285	0.386	0.335	0.254	0.338	0.751	0.119	NA
us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType us-gaap:Equipment		NA	NA	9.902	NA	NA	NA	8.168	8.036	7.536	7.4	6.628	6.459	6.197	5.562	5.053	NA
us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType us-gaap:FurnitureAndFixtures		NA	NA	1.521	NA	NA	NA	1.165	1.12	1.04	0.862	0.813	0.771	0.73	0.661	0.625	NA
us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType us-gaap:LeaseholdImprovements		NA	NA	11.111	NA	NA	NA	10.834	10.834	10.834	10.828	10.828	10.828	10.824	9.514	9.28	NA
us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment		NA	NA	14.288	NA	NA	NA	11.221	10.365	9.479	8.596	7.643	6.696	5.722	4.806	3.978	NA
us-gaap:PropertyPlantAndEquipmentNet	█▄▂▁▁▁▁▂▂▂▂▃▃▃▂	23.806	14.849	10.807	8.728	8.264	8.761	9.33	10.011	10.362	11.026	11.107	11.762	12.513	11.813	11.23	NA
us-gaap:OperatingLeaseRightOfUseAsset	█▁▁	36.137	12.243	12.781	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:OtherAssetsNoncurrent	▇██▃▂▂▂▁▁▁▁▁▁▁▃	5.775	6.183	6.246	2.245	1.323	0.963	0.872	0.263	0.319	0.315	0.284	0.205	0.205	0.205	1.502	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:AccountsPayableCurrent	▆█▅▃▄▁▂▁▁▁▁▁▂▂▂	16.957	24.544	15.682	8.102	12.052	2.426	4.704	2.905	2.448	2.829	3.102	2.109	5.388	3.92	3.82	NA
us-gaap:AccruedLiabilitiesCurrent	▅▃▅▃▂▅▅▅█▄▃▃▂▁▁	9.706	7.536	9.543	7.496	5.611	10.17	9.522	9.662	15.552	7.629	6.023	6.667	4.342	3.61	3.137	NA
us-gaap:ContractWithCustomerLiabilityCurrent	▅▅▅█▁▁▁▁▁▁	74.571	74.571	74.571	115.614	7.0	7.0	7.0	7.0	7.0	7.0	NA	NA	NA	NA	NA	NA
us-gaap:LiabilitiesCurrent	▆▇▆█▂▁▁▁▂▁▁▁▁▁▁	130.37	132.055	121.669	162.871	40.025	21.004	22.706	21.057	26.513	19.003	16.935	16.611	16.38	14.262	12.726	NA
us-gaap:OperatingLeaseLiabilityCurrent	▄	2.5	NA	2.9	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:OtherAccruedLiabilitiesCurrent		NA	NA	9.543	0.617	1.194	0.483	0.196	0.121	0.073	0.193	0.163	0.186	0.258	0.3	0.212	NA
us-gaap:OtherLiabilitiesCurrent	▁▅██▃▃▃▃▃▄▄▄▄▄▂	0.38	2.381	3.566	3.422	1.463	1.408	1.48	1.49	1.513	1.545	1.56	1.585	1.65	1.732	0.769	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:OtherLiabilitiesNoncurrent	███▇▁▁▁▁▂▂▂▂▂▂▁	10.199	10.199	10.246	8.178	0.693	0.64	0.806	1.026	1.283	1.543	1.792	2.047	2.308	2.554	0.565	NA
us-gaap:OperatingLeaseLiabilityNoncurrent	█▁▁	49.741	14.706	15.243	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	▄	5.908	NA	4.041	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree	▄	6.101	NA	3.409	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour	▄	6.302	NA	3.522	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive		NA	NA	3.64	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:StockholdersEquity	▇█▆▇▆▃▃▃▄▄▄▄▄▄▁	604.555	664.79	502.304	544.417	428.71	140.638	163.842	177.227	196.646	221.567	234.942	245.121	254.574	266.591	-72.328	NA
us-gaap:CommonStockValue	██▆▆▆▁▁▁▁▁▁	0.007	0.007	0.006	0.006	0.006	0.004	0.004	0.004	0.004	0.004	0.004	NA	NA	NA	NA	NA
us-gaap:AdditionalPaidInCapital	██▆▆▆▃▃▃▃▃▃▃▃▃▁	1081.341	1065.562	830.438	820.661	706.713	373.425	369.1	365.898	362.905	359.82	357.873	355.758	354.375	352.872	0.948	NA
us-gaap:RetainedEarningsAccumulatedDeficit	▁▂▄▄▄▅▆▆▆▇▇▇███	-476.747	-400.777	-328.184	-276.331	-278.153	-233.079	-205.326	-188.728	-166.376	-138.286	-122.828	-110.533	-99.722	-86.188	-73.234	NA
us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax	▂▃▄▄▅█▄▄▅▃▁▁▁▁▂	-0.046	-0.002	0.044	0.081	0.144	0.288	0.064	0.053	0.113	0.029	-0.107	-0.108	-0.083	-0.097	-0.042	NA
us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName,us-gaap:StatementEquityComponents,us-gaap:TypeOfArrangement rcus:GileadSciencesInc,us-gaap:AdditionalPaidInCapital,rcus:CommonStockPurchaseAgreement		NA	220.295	NA	107.468	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName,us-gaap:StatementEquityComponents,us-gaap:TypeOfArrangement rcus:GileadSciencesInc,us-gaap:CommonStock,rcus:CommonStockPurchaseAgreement		NA	0.001	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName,us-gaap:SubsequentEventType,us-gaap:TypeOfArrangement rcus:GileadSciencesInc,us-gaap:SubsequentEvent,rcus:CommonStockPurchaseAgreement		NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName,us-gaap:TypeOfArrangement rcus:GileadSciencesInc,rcus:CommonStockPurchaseAgreement		NA	220.296	NA	107.468	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:RelatedPartyTransactionsByRelatedParty,us-gaap:TypeOfArrangement rcus:GileadSciencesInc,rcus:CommonStockPurchaseAgreement	▁█	0.0	327.8	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	█▁	13.367	12.761	NA	6.002	4.47	3.462	NA	2.74	2.13	1.674	NA	1.048	1.116	0.656	NA	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:NetCashProvidedByUsedInOperatingActivities	▁▁▂█▂▂▃▂▂▂▃▃▃▂▃▂	-73.995	-66.316	-49.88	216.265	-23.938	-31.277	-9.471	-27.399	-19.753	-16.839	-7.107	-11.765	-10.877	-13.247	15.587	-24.234
us-gaap:NetCashProvidedByUsedInInvestingActivities	▇█▇▁▆█▇▇▇▇▇▆▇▇▆▇	3.003	62.826	-0.231	-387.119	-87.073	40.056	-12.104	30.364	26.673	14.279	2.511	-83.337	-16.123	-16.491	-42.066	12.731
us-gaap:NetCashProvidedByUsedInFinancingActivities	▁▆▁▃█▁▁▁▁▁▁▁▁▄▃▁	2.231	222.12	1.677	107.518	328.87	0.61	0.52	-0.041	0.649	-0.005	0.771	-0.007	-1.118	129.428	106.599	0.189
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	▂█▂▂█▃▃▃▃▃▃▁▂▅	-68.761	218.63	-48.434	-63.336	217.859	9.389	-21.055	2.924	7.569	-2.565	-3.825	-95.109	-28.118	99.69	NA	NA

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:IncreaseDecreaseInAccountsPayable	▁█▇▄█▄▆▅▅▅▅▄▅▅▆▅	-11.291	7.722	6.107	-3.503	9.01	-2.342	1.82	0.472	-0.049	-0.517	0.96	-2.376	1.653	-0.306	2.039	-0.696
us-gaap:NetCashProvidedByUsedInOperatingActivities	▁▁▂█▂▂▃▂▂▂▃▃▃▂▃▂	-73.995	-66.316	-49.88	216.265	-23.938	-31.277	-9.471	-27.399	-19.753	-16.839	-7.107	-11.765	-10.877	-13.247	15.587	-24.234
us-gaap:NetIncomeLoss	▁▁▃█▄▅▆▆▅▆▇▇▇▇▇▆	-75.97	-72.593	-51.853	1.822	-45.074	-27.753	-16.598	-22.352	-28.09	-17.67	-12.295	-10.812	-13.533	-12.954	-13.21	-23.122
us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents us-gaap:RetainedEarnings	▁█	-75.97	-72.593	NA	1.822	-45.074	-27.753	NA	-22.352	-28.09	-17.67	NA	-10.812	-13.533	-12.954	NA	NA
us-gaap:ProfitLoss	▁▁▃█▄▅▆▆▅▆▇▇▇▇▇	-75.97	-72.593	-51.853	1.822	-45.074	-27.753	-16.598	-22.352	-28.09	-17.67	-12.295	-10.811	-13.534	-12.954	-13.21	NA
us-gaap:ShareBasedCompensation	██▅▄▃▃▂▂▂▂▁▁▂▁▁▁	13.367	12.761	7.891	6.002	4.47	3.462	2.437	2.74	2.13	1.674	1.054	1.048	1.116	0.656	0.155	0.137

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:NetCashProvidedByUsedInInvestingActivities	▇█▇▁▆█▇▇▇▇▇▆▇▇▆▇	3.003	62.826	-0.231	-387.119	-87.073	40.056	-12.104	30.364	26.673	14.279	2.511	-83.337	-16.123	-16.491	-42.066	12.731
us-gaap:PaymentsToAcquirePropertyPlantAndEquipment	█▅▃▂▁▁▁▁▁▂▁▂▂▂▁▂	6.073	3.641	1.519	1.071	0.256	0.209	0.196	0.55	0.551	0.628	0.258	1.127	1.304	1.054	0.294	0.839
us-gaap:PaymentsToAcquireInvestments	▄▄▄█▃▁▂▂▂▂▂▃▂▂▂▁	178.292	192.398	170.755	429.214	130.804	8.885	67.51	56.408	51.43	72.407	39.485	131.396	49.587	41.084	59.112	6.278

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
us-gaap:NetCashProvidedByUsedInFinancingActivities	▁▆▁▃█▁▁▁▁▁▁▁▁▄▃▁	2.231	222.12	1.677	107.518	328.87	0.61	0.52	-0.041	0.649	-0.005	0.771	-0.007	-1.118	129.428	106.599	0.189

		2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30

Common Stock Value

us-gaap:CommonStockValue

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31
Value	7000.0	7000.0	6000.0	6000.0	6000.0	4000.0	4000.0	4000.0	4000.0	4000.0	4000.0
Percentage of CommonStockValue	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Weighted Average Number Of Diluted Shares Outstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30
Value	63	65	48	44	43
Percentage of WeightedAverageNumberOfDilutedSharesOutstanding	100.0	100.0	100.0	100.0	100.0

Weighted Average Number Of Shares Outstanding Basic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31	2017-09-30	2017-06-30	2017-03-31
Value	63	62	50	45	45	45	44	44	44	11	3.994915	3.900271	3.549791
Percentage of WeightedAverageNumberOfSharesOutstandingBasic	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Weighted Average Number Of Share Outstanding Basic And Diluted

us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	69	67	48	44	44	43	43	43	43	42	42	9.488352	2.208065	1.949258	1.69315	1.452215
Percentage of WeightedAverageNumberOfShareOutstandingBasicAndDiluted	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic

Period End	2020-09-30	2019-09-30
Value	0.03	-0.51
Percentage of EarningsPerShareBasic	100.0	100.0

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted

Period End	2020-09-30	2019-09-30
Value	0.03	-0.51
Percentage of EarningsPerShareDiluted	100.0	100.0

Earnings Per Share Basic And Diluted

us-gaap:EarningsPerShareBasicAndDiluted

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-1.09	-1.08	-0.93	-0.63	-0.37	-0.51	-0.64	-0.41	-0.27	-0.25	-0.32	-1.37	-5.56	-11.86	-5.64	-4.96
Percentage of EarningsPerShareBasicAndDiluted	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Income Loss From Continuing Operations Per Basic Share

us-gaap:IncomeLossFromContinuingOperationsPerBasicShare

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30
Value	-0.82	0.03	-0.93	-0.63	-0.51
Percentage of IncomeLossFromContinuingOperationsPerBasicShare	100.0	100.0	100.0	100.0	100.0

Income Loss From Continuing Operations Per Diluted Share

us-gaap:IncomeLossFromContinuingOperationsPerDilutedShare

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30
Value	-0.82	0.03	-0.93	-0.63	-0.51
Percentage of IncomeLossFromContinuingOperationsPerDilutedShare	100.0	100.0	100.0	100.0	100.0

Allocated Share Based Compensation Expense

us-gaap:AllocatedShareBasedCompensationExpense

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31	2017-09-30	2017-06-30	2017-03-31
Value	13	12	6.002	4.47	3.462	2.74	2.13	1.674	1.048	1.116	0.656	0.136	0.131	0.072
Percentage of AllocatedShareBasedCompensationExpense	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	141.3	134.9	9.3	255.4	197.8	156.6	121.7	95.7	24.4	89.3	52.5	83.4	0.0	0.0

us-gaap:AllocatedShareBasedCompensationExpense us-gaap:IncomeStatementLocation

us-gaap:GeneralAndAdministrativeExpense

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31	2017-09-30	2017-06-30	2017-03-31
Value	6.399	6.591	2.927	2.102	1.726	1.762	1.262	0.827	0.41	0.415	0.316	0.063	0.064	0.031
Percentage of AllocatedShareBasedCompensationExpense	47.9	51.6	48.8	47.0	49.9	64.3	59.2	49.4	39.1	37.2	48.2	46.3	48.9	43.1
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	67.6	69.7	4.5	120.1	98.6	100.7	72.1	47.3	9.6	33.2	25.3	38.7	0.0	0.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:GeneralAndAdministrativeExpense	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

us-gaap:ResearchAndDevelopmentExpense

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31	2017-09-30	2017-06-30	2017-03-31
Value	6.968	6.17	3.075	2.368	1.736	0.978	0.868	0.847	0.638	0.701	0.34	0.073	0.067	0.041
Percentage of AllocatedShareBasedCompensationExpense	52.1	48.4	51.2	53.0	50.1	35.7	40.8	50.6	60.9	62.8	51.8	53.7	51.1	56.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	73.6	65.2	4.8	135.3	99.2	55.9	49.6	48.4	14.9	56.1	27.2	44.8	0.0	0.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ResearchAndDevelopmentExpense	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

Comprehensive Income Net Of Tax

us-gaap:ComprehensiveIncomeNetOfTax

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-76014000.0	-72639000.0	-51890000.0	1759000.0	-45218000.0	-27529000.0	-16587000.0	-22411000.0	-28006000.0	-17534000.0	-12294000.0	-10837000.0	-13519000.0	-13009000.0	-13243000.0	-23108000.0	-9539000.0	-7208000.0
Percentage of ComprehensiveIncomeNetOfTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.4	-767.8	-547.0	2.7	-2583.9	-1573.1	-170.1	-1280.6	-1600.3	-1001.9	-787.1	-252.6	-1081.5	-1040.7	-1059.4	-14176.7	0.0	0.0

General And Administrative Expense

us-gaap:GeneralAndAdministrativeExpense

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	16	15	12	11	11	7.008	6.591	7.758	5.911	4.969	3.61	3.577	3.45	2.929	2.448	1.862	1.83	1.496
Percentage of GeneralAndAdministrativeExpense	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	177.8	167.2	134.8	17.3	653.3	400.5	67.6	443.3	337.8	283.9	231.1	83.4	276.0	234.3	195.8	1142.3	0.0	0.0

Net Income Loss

us-gaap:NetIncomeLoss

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-75970000.0	-72593000.0	-51853000.0	1822000.0	-45074000.0	-27753000.0	-16598000.0	-22352000.0	-28090000.0	-17670000.0	-12295000.0	-10812000.0	-13533000.0	-12954000.0	-13210000.0	-23122000.0	-9550000.0	-7200000.0
Percentage of NetIncomeLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.0	-767.3	-546.6	2.8	-2575.7	-1585.9	-170.2	-1277.3	-1605.1	-1009.7	-787.1	-252.0	-1082.6	-1036.3	-1056.8	-14185.3	0.0	0.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	-75970000.0	-72593000.0	1822000.0	-45074000.0	-27753000.0	-22352000.0	-28090000.0	-17670000.0	-10812000.0	-13533000.0	-12954000.0
Percentage of NetIncomeLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.0	-767.3	2.8	-2575.7	-1585.9	-1277.3	-1605.1	-1009.7	-252.0	-1082.6	-1036.3
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RetainedEarnings	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Nonoperating Income Expense

us-gaap:NonoperatingIncomeExpense

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	166000.0	154000.0	159000.0	270000.0	301000.0	647000.0	929000.0	897000.0	1070000.0	1103000.0	1189000.0	1333000.0	2366000.0	377000.0	134000.0	12000.0	114000.0	100000.0
Percentage of NonoperatingIncomeExpense	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	1.8	1.6	1.7	0.4	17.2	37.0	9.5	51.3	61.1	63.0	76.1	31.1	189.3	30.2	10.7	7.4	0.0	0.0

Operating Expenses

us-gaap:OperatingExpenses

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	85	82	61	62	47	30	27	24	30	20	15	16	17	14	14	23	9.664	7.3
Percentage of OperatingExpenses	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	904.7	868.9	648.2	97.6	2692.9	1722.9	279.8	1428.5	1766.3	1172.7	963.3	383.0	1371.9	1166.5	1167.5	14292.6	0.0	0.0

Operating Income Loss

us-gaap:OperatingIncomeLoss

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-76136000.0	-72747000.0	-52012000.0	1552000.0	-45375000.0	-28400000.0	-17527000.0	-23249000.0	-29160000.0	-18773000.0	-13484000.0	-12145000.0	-15899000.0	-13331000.0	-13344000.0	-23134000.0	-9664000.0	-7300000.0
Percentage of OperatingIncomeLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-804.7	-768.9	-548.2	2.4	-2592.9	-1622.9	-179.8	-1328.5	-1666.3	-1072.7	-863.3	-283.0	-1271.9	-1066.5	-1067.5	-14192.6	0.0	0.0

Other Comprehensive Income Loss Net Of Tax

us-gaap:OtherComprehensiveIncomeLossNetOfTax

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	-44000.0	-46000.0	-63000.0	-144000.0	224000.0	-60000.0	84000.0	136000.0	-25000.0	14000.0	-55000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-0.5	-0.5	-0.1	-8.2	12.8	-3.4	4.8	7.8	-0.6	1.1	-4.4

us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	-44000.0	-46000.0	-63000.0	-144000.0	224000.0	-60000.0	84000.0	136000.0	-25000.0	14000.0	-55000.0
Percentage of OtherComprehensiveIncomeLossNetOfTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-0.5	-0.5	-0.1	-8.2	12.8	-3.4	4.8	7.8	-0.6	1.1	-4.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:AccumulatedOtherComprehensiveIncome	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Profit Loss

us-gaap:ProfitLoss

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	-75970000.0	-72593000.0	-51853000.0	1822000.0	-45074000.0	-27753000.0	-16598000.0	-22352000.0	-28090000.0	-17670000.0	-12295000.0	-10811000.0	-13534000.0	-12954000.0	-13210000.0
Percentage of ProfitLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.0	-767.3	-546.6	2.8	-2575.7	-1585.9	-170.2	-1277.3	-1605.1	-1009.7	-787.1	-251.9	-1082.7	-1036.3	-1056.8

Research And Development Expense

us-gaap:ResearchAndDevelopmentExpense

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	68	66	48	51	35	23	20	17	24	15	11	12	13	11	12	21	7.834	5.804
Percentage of ResearchAndDevelopmentExpense	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	726.9	701.7	513.5	80.3	2039.6	1322.4	212.2	985.2	1428.5	888.8	732.1	299.7	1095.9	932.2	971.7	13150.3	0.0	0.0

us-gaap:ResearchAndDevelopmentExpense us-gaap:CounterpartyName

rcus:Genentech

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31
Value	0.3	0.3	0.4	0.1	0.0	0.0
Percentage of ResearchAndDevelopmentExpense	0.4	0.5	0.8	0.2	0.0	0.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	3.2	3.2	4.2	0.2	0.0	0.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:Genentech	0.0	0.0	0.0	0.0	0.0	0.0

Research And Development Expense Excluding Acquired In Process Cost

us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost

rcus:StrataOncologyInc, rcus:StrataAgreement

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31
Value	500000.0	600000.0	300000.0	600000.0	400000.0
Percentage of ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	5.3	6.3	0.5	34.3	22.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:StrataOncologyInc rcus:StrataAgreement	0.0	0.0	0.0	0.0	0.0

us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost us-gaap:TypeOfArrangement

rcus:AstraZenecaAgreement

Period End	2021-06-30
Value	300000.0
Percentage of ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost	60.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	3.2
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:AstraZenecaAgreement	0.0

Revenue From Contract With Customer Excluding Assessed Tax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	9.461	9.461	9.487	64	1.75	1.75	9.75	1.75	1.75	1.75	1.562	4.291	1.25	1.25	1.25	0.163
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService

rcus:GileadAccessRights

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	7.711	7.711	7.737	7.684
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	81.5	81.5	81.6	11.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	81.5	81.5	81.6	11.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:GileadAccessRights	100.0	100.0	100.0	100.0

rcus:GileadLicenseToZimberelimab

Period End	2020-12-31	2020-09-30
Value	0.0	55
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	0.0	85.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	0.0	85.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:GileadLicenseToZimberelimab	0.0	100.0

Revenues

us-gaap:Revenues

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	9.461	9.461	9.487	64	1.75	1.75	9.75	1.75	1.75	1.75	1.562	4.291	1.25	1.25	1.25	0.163
Percentage of Revenues	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:Revenues us-gaap:CounterpartyName, us-gaap:ProductOrService

rcus:GileadSciencesIncAndTaihoPharmaceuticalCo, rcus:Collaboration

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30
Value	9.461	9.461	9.487	9.434	1.75	1.75	1.75	1.75
Percentage of Revenues	100.0	100.0	100.0	14.6	100.0	100.0	17.9	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	100.0	100.0	100.0	14.6	100.0	100.0	17.9	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:GileadSciencesIncAndTaihoPharmaceuticalCo rcus:Collaboration	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

rcus:GileadSciencesIncAndTaihoPharmaceuticalCo, us-gaap:License

Period End	2020-12-31	2020-09-30
Value	0.0	55
Percentage of Revenues	0.0	85.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	0.0	85.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:GileadSciencesIncAndTaihoPharmaceuticalCo us-gaap:License	0.0	0.0

rcus:GileadSciencesIncAndTaihoPharmaceuticalCo, us-gaap:LicenseAndService

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30
Value	9.461	9.461	9.487	64	1.75	1.75	9.75	1.75
Percentage of Revenues	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax rcus:GileadSciencesIncAndTaihoPharmaceuticalCo us-gaap:LicenseAndService	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Assets

us-gaap:Assets

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	898	935	772	811	481	176	203	216	238	258	274	286	293	305	190
Percentage of Assets	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Liabilities

us-gaap:Liabilities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	294	270	269	266	52	35	39	39	42	36	39	41	39	38	36
Percentage of Liabilities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	32.7	28.9	35.0	32.9	10.9	20.2	19.3	18.3	17.7	14.3	14.5	14.5	13.4	12.7	19.2

Liabilities And Stockholders Equity

us-gaap:LiabilitiesAndStockholdersEquity

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	898	935	772	811	481	176	203	216	238	258	274	286	293	305	190
Percentage of LiabilitiesAndStockholdersEquity	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Stockholders Equity

us-gaap:StockholdersEquity

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31	2015-12-31
Value	604	664	502	544	428	140	163	177	196	221	234	245	254	266	-72.328	-19.994	-2.171
Percentage of StockholdersEquity	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	67.3	71.1	65.0	67.1	89.1	79.8	80.7	81.7	82.3	85.7	85.5	85.5	86.6	87.3	-38.0	0.0	0.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31
Value	-0.046	-0.002	0.044	0.081	0.144	0.288	0.064	0.053	0.113	0.029	-0.107	-0.108	-0.083	-0.097	-0.042	-0.026
Percentage of StockholdersEquity	-0.0	-0.0	0.0	0.0	0.0	0.2	0.0	0.0	0.1	0.0	-0.0	-0.0	-0.0	-0.0	0.1	0.1
Percentage of Assets	-0.0	-0.0	0.0	0.0	0.0	0.2	0.0	0.0	0.0	0.0	-0.0	-0.0	-0.0	-0.0	-0.0	0.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome	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	0.0

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31	2015-12-31
Value	1081	1065	830	820	706	373	369	365	362	359	357	355	354	352	0.948	0.184	0.011
Percentage of StockholdersEquity	178.9	160.3	165.3	150.7	164.8	265.5	225.3	206.5	184.5	162.4	152.3	145.1	139.2	132.4	-1.3	-0.9	-0.5
Percentage of Assets	120.3	113.9	107.5	101.2	146.8	212.0	181.7	168.7	151.9	139.2	130.2	124.1	120.6	115.5	0.5	0.0	0.0
Percentage of Assets us-gaap:AdditionalPaidInCapital	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	0.0	0.0

us-gaap:CommonStock

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31
Value	0.007	0.007	0.006	0.006	0.006	0.004	0.004	0.004	0.004	0.004	0.004	0.004	0.004	0.004
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
Percentage of Assets	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
Percentage of Assets us-gaap:CommonStock	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

us-gaap:RetainedEarnings

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31	2015-12-31
Value	-476.747	-400.777	-328.184	-276.331	-278.153	-233.079	-205.326	-188.728	-166.376	-138.286	-122.828	-110.534	-99.722	-86.188	-73.234	-20.152	-2.182
Percentage of StockholdersEquity	-78.9	-60.3	-65.3	-50.8	-64.9	-165.7	-125.3	-106.5	-84.6	-62.4	-52.3	-45.1	-39.2	-32.3	101.3	100.8	100.5
Percentage of Assets	-53.0	-42.9	-42.5	-34.1	-57.8	-132.3	-101.1	-87.0	-69.6	-53.5	-44.7	-38.6	-33.9	-28.2	-38.4	0.0	0.0
Percentage of Assets us-gaap:RetainedEarnings	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	0.0	0.0

Assets Current

us-gaap:AssetsCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	745	841	735	797	471	166	192	200	227	245	258	265	267	282	176
Percentage of AssetsCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	83.0	90.0	95.3	98.3	98.0	94.4	94.9	92.4	95.3	94.8	94.2	92.5	91.0	92.4	92.9

Cash And Cash Equivalents At Carrying Value

us-gaap:CashAndCashEquivalentsAtCarryingValue

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31	2016-12-31	2015-12-31
Value	320	390	173	221	285	67	57	78	76	68	71	74	169	198	98	18	29	39	65	46
Percentage of CashAndCashEquivalentsAtCarryingValue	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	35.7	41.7	22.5	27.4	59.2	38.2	28.5	36.4	31.8	26.5	25.8	26.1	57.8	64.9	51.7	0.0	0.0	0.0	0.0	0.0

Prepaid Expense And Other Assets Current

us-gaap:PrepaidExpenseAndOtherAssetsCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	21	8.68	5.471	11	8.665	8.007	4.303	4.223	3.273	3.08	2.321	2.329	1.55	1.834	1.141
Percentage of PrepaidExpenseAndOtherAssetsCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	2.4	0.9	0.7	1.5	1.8	4.5	2.1	1.9	1.4	1.2	0.8	0.8	0.5	0.6	0.6

Property Plant And Equipment Gross

us-gaap:PropertyPlantAndEquipmentGross

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	25	20	20	19	19	18	18	18	16	15
Percentage of PropertyPlantAndEquipmentGross	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	3.2	10.1	9.4	8.3	7.6	6.8	6.4	6.2	5.4	8.0

us-gaap:PropertyPlantAndEquipmentGross us-gaap:PropertyPlantAndEquipmentByType

rcus:CapitalizedSoftware

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	0.225	0.146	0.146	0.146	0.146	0.146	0.146	0.146	0.131	0.131
Percentage of PropertyPlantAndEquipmentGross	0.9	0.7	0.7	0.7	0.7	0.8	0.8	0.8	0.8	0.9
Percentage of Assets	0.0	0.1	0.1	0.1	0.1	0.1	0.1	0.0	0.0	0.1
Percentage of Assets rcus:CapitalizedSoftware	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

us-gaap:ConstructionInProgress

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	2.336	0.238	0.24	0.285	0.386	0.335	0.254	0.338	0.751	0.119
Percentage of PropertyPlantAndEquipmentGross	9.3	1.2	1.2	1.4	2.0	1.8	1.4	1.9	4.5	0.8
Percentage of Assets	0.3	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.2	0.1
Percentage of Assets us-gaap:ConstructionInProgress	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

us-gaap:Equipment

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	9.902	8.168	8.036	7.536	7.4	6.628	6.459	6.197	5.562	5.053
Percentage of PropertyPlantAndEquipmentGross	39.5	39.7	39.4	38.0	37.7	35.3	35.0	34.0	33.5	33.2
Percentage of Assets	1.3	4.0	3.7	3.2	2.9	2.4	2.3	2.1	1.8	2.7
Percentage of Assets us-gaap:Equipment	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

us-gaap:FurnitureAndFixtures

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	1.521	1.165	1.12	1.04	0.862	0.813	0.771	0.73	0.661	0.625
Percentage of PropertyPlantAndEquipmentGross	6.1	5.7	5.5	5.2	4.4	4.3	4.2	4.0	4.0	4.1
Percentage of Assets	0.2	0.6	0.5	0.4	0.3	0.3	0.3	0.2	0.2	0.3
Percentage of Assets us-gaap:FurnitureAndFixtures	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

us-gaap:LeaseholdImprovements

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	11	10	10	10	10	10	10	10	9.514	9.28
Percentage of PropertyPlantAndEquipmentGross	44.3	52.7	53.2	54.6	55.2	57.7	58.7	59.4	57.2	61.0
Percentage of Assets	1.4	5.3	5.0	4.5	4.2	3.9	3.8	3.7	3.1	4.9
Percentage of Assets us-gaap:LeaseholdImprovements	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Accumulated Depreciation Depletion And Amortization Property Plant And Equipment

us-gaap:AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	14	11	10	9.479	8.596	7.643	6.696	5.722	4.806	3.978
Percentage of AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	1.9	5.5	4.8	4.0	3.3	2.8	2.3	1.9	1.6	2.1

Property Plant And Equipment Net

us-gaap:PropertyPlantAndEquipmentNet

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	23	14	10	8.728	8.264	8.761	9.33	10	10	11	11	11	12	11	11
Percentage of PropertyPlantAndEquipmentNet	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	2.6	1.6	1.4	1.1	1.7	5.0	4.6	4.6	4.3	4.3	4.0	4.1	4.3	3.9	5.9

Operating Lease Right Of Use Asset

us-gaap:OperatingLeaseRightOfUseAsset

Period End	2021-06-30	2021-03-31	2020-12-31
Value	36	12	12
Percentage of OperatingLeaseRightOfUseAsset	100.0	100.0	100.0
Percentage of Assets	4.0	1.3	1.7

Other Assets Noncurrent

us-gaap:OtherAssetsNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	5775000.0	6183000.0	6246000.0	2245000.0	1323000.0	963000.0	872000.0	263000.0	319000.0	315000.0	284000.0	205000.0	205000.0	205000.0	1502000.0
Percentage of OtherAssetsNoncurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	0.6	0.7	0.8	0.3	0.3	0.5	0.4	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.8

Accounts Payable Current

us-gaap:AccountsPayableCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	16	24	15	8.102	12	2.426	4.704	2.905	2.448	2.829	3.102	2.109	5.388	3.92	3.82
Percentage of AccountsPayableCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	1.9	2.6	2.0	1.0	2.5	1.4	2.3	1.3	1.0	1.1	1.1	0.7	1.8	1.3	2.0

Accrued Liabilities Current

us-gaap:AccruedLiabilitiesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	9.706	7.536	9.543	7.496	5.611	10	9.522	9.662	15	7.629	6.023	6.667	4.342	3.61	3.137
Percentage of AccruedLiabilitiesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	1.1	0.8	1.2	0.9	1.2	5.8	4.7	4.5	6.5	3.0	2.2	2.3	1.5	1.2	1.6

Contract With Customer Liability Current

us-gaap:ContractWithCustomerLiabilityCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31
Value	74	74	74	115	7.0	7.0	7.0	7.0	7.0	7.0
Percentage of ContractWithCustomerLiabilityCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	8.3	8.0	9.7	14.3	1.5	4.0	3.4	3.2	2.9	2.7

Liabilities Current

us-gaap:LiabilitiesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	130	132	121	162	40	21	22	21	26	19	16	16	16	14	12
Percentage of LiabilitiesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	14.5	14.1	15.8	20.1	8.3	11.9	11.2	9.7	11.1	7.4	6.2	5.8	5.6	4.7	6.7

Operating Lease Liability Current

us-gaap:OperatingLeaseLiabilityCurrent

Period End	2021-06-30	2020-12-31
Value	2500000.0	2900000.0
Percentage of OperatingLeaseLiabilityCurrent	100.0	100.0
Percentage of Assets	0.3	0.4

Other Accrued Liabilities Current

us-gaap:OtherAccruedLiabilitiesCurrent

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	9543000.0	617000.0	1194000.0	483000.0	196000.0	121000.0	73000.0	193000.0	163000.0	186000.0	258000.0	300000.0	212000.0
Percentage of OtherAccruedLiabilitiesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	1.2	0.1	0.2	0.3	0.1	0.1	0.0	0.1	0.1	0.1	0.1	0.1	0.1

Other Liabilities Current

us-gaap:OtherLiabilitiesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	380000.0	2381000.0	3566000.0	3422000.0	1463000.0	1408000.0	1480000.0	1490000.0	1513000.0	1545000.0	1560000.0	1585000.0	1650000.0	1732000.0	769000.0
Percentage of OtherLiabilitiesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	0.0	0.3	0.5	0.4	0.3	0.8	0.7	0.7	0.6	0.6	0.6	0.6	0.6	0.6	0.4

Other Liabilities Noncurrent

us-gaap:OtherLiabilitiesNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	10	10	10	8.178	0.693	0.64	0.806	1.026	1.283	1.543	1.792	2.047	2.308	2.554	0.565
Percentage of OtherLiabilitiesNoncurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	1.1	1.1	1.3	1.0	0.1	0.4	0.4	0.5	0.5	0.6	0.7	0.7	0.8	0.8	0.3

Operating Lease Liability Noncurrent

us-gaap:OperatingLeaseLiabilityNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31
Value	49	14	15
Percentage of OperatingLeaseLiabilityNoncurrent	100.0	100.0	100.0
Percentage of Assets	5.5	1.6	2.0

Lessee Operating Lease Liability Payments Due Year Two

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearTwo

Period End	2021-06-30	2020-12-31
Value	5908000.0	4041000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	100.0	100.0
Percentage of Assets	0.7	0.5

Lessee Operating Lease Liability Payments Due Year Three

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearThree

Period End	2021-06-30	2020-12-31
Value	6101000.0	3409000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearThree	100.0	100.0
Percentage of Assets	0.7	0.4

Lessee Operating Lease Liability Payments Due Year Four

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFour

Period End	2021-06-30	2020-12-31
Value	6302000.0	3522000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFour	100.0	100.0
Percentage of Assets	0.7	0.5

Lessee Operating Lease Liability Payments Due Year Five

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueYearFive

Period End	2020-12-31
Value	3640000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearFive	100.0
Percentage of Assets	0.5

Operating Lease Liability

us-gaap:OperatingLeaseLiability

Period End	2021-06-30	2020-12-31
Value	52	18
Percentage of OperatingLeaseLiability	100.0	100.0
Percentage of Assets	5.8	2.3

Lessee Operating Lease Liability Payments Due

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue

Period End	2021-06-30	2020-12-31
Value	68	22
Percentage of LesseeOperatingLeaseLiabilityPaymentsDue	100.0	100.0
Percentage of Assets	7.6	2.9

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDue us-gaap:StatementGeographical

rcus:BrisbaneCalifornia

Period End	2021-06-30
Value	90
Percentage of LesseeOperatingLeaseLiabilityPaymentsDue	131.3
Percentage of Assets	10.0
Percentage of Assets rcus:BrisbaneCalifornia	0.0

stpr:CA

Period End	2021-06-30
Value	5.3
Percentage of LesseeOperatingLeaseLiabilityPaymentsDue	7.7
Percentage of Assets	0.6
Percentage of Assets stpr:CA	0.0

Lessee Operating Lease Liability Undiscounted Excess Amount

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount

Period End	2021-06-30	2020-12-31
Value	16	4.153
Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	100.0	100.0
Percentage of Assets	1.8	0.5

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount us-gaap:StatementGeographical

rcus:BrisbaneCalifornia

Period End	2020-12-31
Value	90
Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	2174.3
Percentage of Assets	11.7
Percentage of Assets rcus:BrisbaneCalifornia	0.0

us-gaap:LesseeOperatingLeaseLiabilityUndiscountedExcessAmount us-gaap:StatementGeographical, us-gaap:SubsequentEventType

stpr:CA, us-gaap:SubsequentEvent

Period End	2021-04-30
Value	43
Percentage of LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	0.0
Percentage of Assets	0.0
Percentage of Assets stpr:CA us-gaap:SubsequentEvent	0.0

Stockholders Equity

us-gaap:StockholdersEquity

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31	2015-12-31
Value	604	664	502	544	428	140	163	177	196	221	234	245	254	266	-72.328	-19.994	-2.171
Percentage of StockholdersEquity	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	67.3	71.1	65.0	67.1	89.1	79.8	80.7	81.7	82.3	85.7	85.5	85.5	86.6	87.3	-38.0	0.0	0.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31
Value	-0.046	-0.002	0.044	0.081	0.144	0.288	0.064	0.053	0.113	0.029	-0.107	-0.108	-0.083	-0.097	-0.042	-0.026
Percentage of StockholdersEquity	-0.0	-0.0	0.0	0.0	0.0	0.2	0.0	0.0	0.1	0.0	-0.0	-0.0	-0.0	-0.0	0.1	0.1
Percentage of Assets	-0.0	-0.0	0.0	0.0	0.0	0.2	0.0	0.0	0.0	0.0	-0.0	-0.0	-0.0	-0.0	-0.0	0.0
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome	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	0.0

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31	2015-12-31
Value	1081	1065	830	820	706	373	369	365	362	359	357	355	354	352	0.948	0.184	0.011
Percentage of StockholdersEquity	178.9	160.3	165.3	150.7	164.8	265.5	225.3	206.5	184.5	162.4	152.3	145.1	139.2	132.4	-1.3	-0.9	-0.5
Percentage of Assets	120.3	113.9	107.5	101.2	146.8	212.0	181.7	168.7	151.9	139.2	130.2	124.1	120.6	115.5	0.5	0.0	0.0
Percentage of Assets us-gaap:AdditionalPaidInCapital	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	0.0	0.0

us-gaap:CommonStock

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31
Value	0.007	0.007	0.006	0.006	0.006	0.004	0.004	0.004	0.004	0.004	0.004	0.004	0.004	0.004
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
Percentage of Assets	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
Percentage of Assets us-gaap:CommonStock	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

us-gaap:RetainedEarnings

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2016-12-31	2015-12-31
Value	-476.747	-400.777	-328.184	-276.331	-278.153	-233.079	-205.326	-188.728	-166.376	-138.286	-122.828	-110.534	-99.722	-86.188	-73.234	-20.152	-2.182
Percentage of StockholdersEquity	-78.9	-60.3	-65.3	-50.8	-64.9	-165.7	-125.3	-106.5	-84.6	-62.4	-52.3	-45.1	-39.2	-32.3	101.3	100.8	100.5
Percentage of Assets	-53.0	-42.9	-42.5	-34.1	-57.8	-132.3	-101.1	-87.0	-69.6	-53.5	-44.7	-38.6	-33.9	-28.2	-38.4	0.0	0.0
Percentage of Assets us-gaap:RetainedEarnings	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	0.0	0.0

Common Stock Value

us-gaap:CommonStockValue

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31
Value	7000.0	7000.0	6000.0	6000.0	6000.0	4000.0	4000.0	4000.0	4000.0	4000.0	4000.0
Percentage of CommonStockValue	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Additional Paid In Capital

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	1081	1065	830	820	706	373	369	365	362	359	357	355	354	352	0.948
Percentage of AdditionalPaidInCapital	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	120.3	113.9	107.5	101.2	146.8	212.0	181.7	168.7	151.9	139.2	130.2	124.1	120.6	115.5	0.5

Retained Earnings Accumulated Deficit

us-gaap:RetainedEarningsAccumulatedDeficit

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	-476750000.0	-400780000.0	-328180000.0	-276330000.0	-278150000.0	-233080000.0	-205330000.0	-188730000.0	-166380000.0	-138290000.0	-122830000.0	-110530000.0	-99722000.0	-86188000.0	-73234000.0
Percentage of RetainedEarningsAccumulatedDeficit	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	-53.0	-42.9	-42.5	-34.1	-57.8	-132.3	-101.1	-87.0	-69.6	-53.5	-44.7	-38.6	-33.9	-28.2	-38.4

Accumulated Other Comprehensive Income Loss Net Of Tax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	-46000.0	-2000.0	44000.0	81000.0	144000.0	288000.0	64000.0	53000.0	113000.0	29000.0	-107000.0	-108000.0	-83000.0	-97000.0	-42000.0
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	-0.0	-0.0	0.0	0.0	0.0	0.2	0.0	0.0	0.0	0.0	-0.0	-0.0	-0.0	-0.0	-0.0

Stock Issued During Period Value New Issues

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName, us-gaap:StatementEquityComponents, us-gaap:TypeOfArrangement

us-gaap:StockIssuedDuringPeriodValueNewIssues

rcus:GileadSciencesInc, us-gaap:AdditionalPaidInCapital, rcus:CommonStockPurchaseAgreement

Period End	2021-03-31	2020-09-30
Value	220	107
Percentage of StockIssuedDuringPeriodValueNewIssues	100.0	100.0
Percentage of Assets	0.0	0.0
Percentage of Assets rcus:GileadSciencesInc us-gaap:AdditionalPaidInCapital rcus:CommonStockPurchaseAgreement	0.0	0.0

rcus:GileadSciencesInc, us-gaap:CommonStock, rcus:CommonStockPurchaseAgreement

Period End	2021-03-31
Value	0.001
Percentage of StockIssuedDuringPeriodValueNewIssues	0.0
Percentage of Assets	0.0
Percentage of Assets rcus:GileadSciencesInc us-gaap:CommonStock rcus:CommonStockPurchaseAgreement	0.0

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName, us-gaap:SubsequentEventType, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, us-gaap:SubsequentEvent, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	200
Percentage of StockIssuedDuringPeriodValueNewIssues	0.0
Percentage of Assets	0.0
Percentage of Assets rcus:GileadSciencesInc us-gaap:SubsequentEvent rcus:CommonStockPurchaseAgreement	0.0

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-02-28	2021-03-31	2020-07-13	2020-09-30
Value	220	220	200	107
Percentage of StockIssuedDuringPeriodValueNewIssues	100.0	0.0	100.0	0.0
Percentage of Assets	0.0	0.0	0.0	0.0
Percentage of Assets rcus:GileadSciencesInc rcus:CommonStockPurchaseAgreement	0.0	0.0	0.0	0.0

us-gaap:StockIssuedDuringPeriodValueNewIssues us-gaap:RelatedPartyTransactionsByRelatedParty, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-06-30	2021-02-28	2021-03-31
Value	0.0	220	327
Percentage of StockIssuedDuringPeriodValueNewIssues	0.0	148.8	0.0
Percentage of Assets	0.0	0.0	0.0
Percentage of Assets rcus:GileadSciencesInc rcus:CommonStockPurchaseAgreement	0.0	0.0	0.0

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

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	13	12	6.002	4.47	3.462	2.74	2.13	1.674	1.048	1.116	0.656
Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

us-gaap:AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	13	12	6.002	4.47	3.462	2.74	2.13	1.674	1.048	1.116	0.656
Percentage of AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of Assets	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Percentage of Assets us-gaap:AdditionalPaidInCapital	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-73.995	-66.316	-49.88	216	-23.938	-31.277	-9.471	-27.399	-19.753	-16.839	-7.107	-11.765	-10.877	-13.247	15	-24.234	-6.815	-9.597
Percentage of NetCashProvidedByUsedInOperatingActivities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-782.1	-700.9	-525.8	335.1	-1367.9	-1787.3	-97.1	-1565.7	-1128.7	-962.2	-455.0	-274.2	-870.2	-1059.8	1247.0	-14867.5	0.0	0.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	3.003	62	-0.231	-387.119	-87.073	40	-12.104	30	26	14	2.511	-83.337	-16.123	-16.491	-42.066	12
Percentage of NetCashProvidedByUsedInInvestingActivities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	31.7	664.1	-2.4	-599.9	-4975.6	2288.9	-124.1	1735.1	1524.2	815.9	160.8	-1942.1	-1289.8	-1319.3	-3365.3	7810.4

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	2.231	222	1.677	107	328	0.61	0.52	-0.041	0.649	-0.005	0.771	-0.007	-1.118	129	106	0.189
Percentage of NetCashProvidedByUsedInFinancingActivities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	23.6	2347.7	17.7	166.6	18792.6	34.9	5.3	-2.3	37.1	-0.3	49.4	-0.2	-89.4	10354.2	8527.9	116.0

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

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31
Value	-68.761	218	-48.434	-63.336	217	9.389	-21.055	2.924	7.569	-2.565	-3.825	-95.109	-28.118	99
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-726.8	2310.9	-510.5	-98.1	12449.1	536.5	-215.9	167.1	432.5	-146.6	-244.9	-2216.5	-2249.4	7975.2

Increase Decrease In Accounts Payable

us-gaap:IncreaseDecreaseInAccountsPayable

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-11291000.0	7722000.0	6107000.0	-3503000.0	9010000.0	-2342000.0	1820000.0	472000.0	-49000.0	-517000.0	960000.0	-2376000.0	1653000.0	-306000.0	2039000.0	-696000.0	1082000.0	-2692000.0
Percentage of IncreaseDecreaseInAccountsPayable	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-73.995	-66.316	-49.88	216	-23.938	-31.277	-9.471	-27.399	-19.753	-16.839	-7.107	-11.765	-10.877	-13.247	15	-24.234	-6.815	-9.597
Percentage of NetCashProvidedByUsedInOperatingActivities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-782.1	-700.9	-525.8	335.1	-1367.9	-1787.3	-97.1	-1565.7	-1128.7	-962.2	-455.0	-274.2	-870.2	-1059.8	1247.0	-14867.5	0.0	0.0

Net Income Loss

us-gaap:NetIncomeLoss

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-75970000.0	-72593000.0	-51853000.0	1822000.0	-45074000.0	-27753000.0	-16598000.0	-22352000.0	-28090000.0	-17670000.0	-12295000.0	-10812000.0	-13533000.0	-12954000.0	-13210000.0	-23122000.0	-9550000.0	-7200000.0
Percentage of NetIncomeLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.0	-767.3	-546.6	2.8	-2575.7	-1585.9	-170.2	-1277.3	-1605.1	-1009.7	-787.1	-252.0	-1082.6	-1036.3	-1056.8	-14185.3	0.0	0.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	-75970000.0	-72593000.0	1822000.0	-45074000.0	-27753000.0	-22352000.0	-28090000.0	-17670000.0	-10812000.0	-13533000.0	-12954000.0
Percentage of NetIncomeLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.0	-767.3	2.8	-2575.7	-1585.9	-1277.3	-1605.1	-1009.7	-252.0	-1082.6	-1036.3
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:RetainedEarnings	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0

Profit Loss

us-gaap:ProfitLoss

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	-75970000.0	-72593000.0	-51853000.0	1822000.0	-45074000.0	-27753000.0	-16598000.0	-22352000.0	-28090000.0	-17670000.0	-12295000.0	-10811000.0	-13534000.0	-12954000.0	-13210000.0
Percentage of ProfitLoss	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	-803.0	-767.3	-546.6	2.8	-2575.7	-1585.9	-170.2	-1277.3	-1605.1	-1009.7	-787.1	-251.9	-1082.7	-1036.3	-1056.8

Share Based Compensation

us-gaap:ShareBasedCompensation

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	13	12	7.891	6.002	4.47	3.462	2.437	2.74	2.13	1.674	1.054	1.048	1.116	0.656	0.155	0.137	0.131	0.072
Percentage of ShareBasedCompensation	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	3.003	62	-0.231	-387.119	-87.073	40	-12.104	30	26	14	2.511	-83.337	-16.123	-16.491	-42.066	12
Percentage of NetCashProvidedByUsedInInvestingActivities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	31.7	664.1	-2.4	-599.9	-4975.6	2288.9	-124.1	1735.1	1524.2	815.9	160.8	-1942.1	-1289.8	-1319.3	-3365.3	7810.4

Payments To Acquire Property Plant And Equipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	6073000.0	3641000.0	1519000.0	1071000.0	256000.0	209000.0	196000.0	550000.0	551000.0	628000.0	258000.0	1127000.0	1304000.0	1054000.0	294000.0	839000.0	2242000.0	2139000.0
Percentage of PaymentsToAcquirePropertyPlantAndEquipment	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Payments To Acquire Investments

us-gaap:PaymentsToAcquireInvestments

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	178	192	170	429	130	8.885	67	56	51	72	39	131	49	41	59	6.278	10	21
Percentage of PaymentsToAcquireInvestments	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	2.231	222	1.677	107	328	0.61	0.52	-0.041	0.649	-0.005	0.771	-0.007	-1.118	129	106	0.189
Percentage of NetCashProvidedByUsedInFinancingActivities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax	23.6	2347.7	17.7	166.6	18792.6	34.9	5.3	-2.3	37.1	-0.3	49.4	-0.2	-89.4	10354.2	8527.9	116.0

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

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31	2016-12-31	2015-12-31
Value	13.88	9.0	7.55	1.71	1.2	0.4
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	100.0	100.0	100.0	100.0	100.0	100.0

Unrecognized Tax Benefits

us-gaap:UnrecognizedTaxBenefits

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31	2016-12-31	2015-12-31
Value	3200000.0	2165000.0	1084000.0	622000.0	242000.0	19000.0
Percentage of UnrecognizedTaxBenefits	100.0	100.0	100.0	100.0	100.0	100.0

Deferred Tax Assets Valuation Allowance

us-gaap:DeferredTaxAssetsValuationAllowance

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31
Value	84	50	30	18
Percentage of DeferredTaxAssetsValuationAllowance	100.0	100.0	100.0	100.0

Proceeds From Sale Of Short Term Investments

us-gaap:ProceedsFromSaleOfShortTermInvestments

Period End	2020-12-31	2018-06-30	2018-03-31	2017-06-30	2017-03-31
Value	0.0	34	25	9.085	7.0
Percentage of ProceedsFromSaleOfShortTermInvestments	0.0	100.0	100.0	100.0	100.0

rcus:AccessRightsRelatedToCompanySResearchAndDevelopmentPipeline

Period End	2020-12-31
Value	0.46
Percentage of AccessRightsRelatedToCompanySResearchAndDevelopmentPipeline	100.0

rcus:AllocationOfTransactionPrice

Period End	2020-12-31
Value	0.874
Percentage of AllocationOfTransactionPrice	100.0

rcus:AllocationToPerformanceObligations

Period End	2020-12-31
Value	0.874
Percentage of AllocationToPerformanceObligations	100.0

rcus:CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	1073000.0	927000.0	526000.0	519000.0
Percentage of CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities	100.0	100.0	100.0	100.0

rcus:ClinicalAndRegulatoryMilestonesAchievedUnderLicenseAgreement us-gaap:CounterpartyName

rcus:ClinicalAndRegulatoryMilestonesAchievedUnderLicenseAgreement

rcus:WuXiBiologicsLicenseAgreement

Period End	2020-12-31
Value	16
Percentage of ClinicalAndRegulatoryMilestonesAchievedUnderLicenseAgreement	100.0

rcus:ClinicalRegulatoryAndCommercializationRemainingMilestonePayments us-gaap:CounterpartyName

rcus:ClinicalRegulatoryAndCommercializationRemainingMilestonePayments

rcus:AbmunoLicenseAgreement

Period End	2021-06-30	2021-03-31
Value	0.0	93
Percentage of ClinicalRegulatoryAndCommercializationRemainingMilestonePayments	0.0	100.0

rcus:ConsultantAndLegalFees us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ConsultantAndLegalFees

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	7300000.0
Percentage of ConsultantAndLegalFees	100.0

rcus:ContractWithCustomerInitialTransactionPrice us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ContractWithCustomerInitialTransactionPrice

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	364
Percentage of ContractWithCustomerInitialTransactionPrice	100.0

rcus:ContractualObligationForFirstPayment us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ContractualObligationForFirstPayment

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	100
Percentage of ContractualObligationForFirstPayment	100.0

rcus:ContractualObligationRemainingAmountNotObligatedToPay us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ContractualObligationRemainingAmountNotObligatedToPay

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	300
Percentage of ContractualObligationRemainingAmountNotObligatedToPay	100.0

rcus:DeferredRevenueFromRelatedParty

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	7.711	7.711	0.0	0.0
Percentage of DeferredRevenueFromRelatedParty	100.0	100.0	0.0	0.0

rcus:DevelopmentAndCommercializationServicesForZimberelimab

Period End	2020-12-31
Value	23000.0
Percentage of DevelopmentAndCommercializationServicesForZimberelimab	100.0

rcus:DirectOfferingCost us-gaap:TypeOfArrangement

rcus:DirectOfferingCost

rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	1900000.0
Percentage of DirectOfferingCost	100.0

rcus:DomvanalimabOption

Period End	2020-12-31
Value	0.088
Percentage of DomvanalimabOption	100.0

rcus:DomvanalimabOptionPaymentUponAchievementOfCertainDevelopmentMilestones us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:DomvanalimabOptionPaymentUponAchievementOfCertainDevelopmentMilestones

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	275
Percentage of DomvanalimabOptionPaymentUponAchievementOfCertainDevelopmentMilestones	100.0

rcus:EtrumadenantOption

Period End	2020-12-31
Value	0.303
Percentage of EtrumadenantOption	100.0

rcus:FairValueOfStockPurchased us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:FairValueOfStockPurchased

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-06-30	2021-03-31	2020-12-31
Value	0.0	109	0.0
Percentage of FairValueOfStockPurchased	0.0	100.0	0.0

rcus:FundsReceivedForStockPurchaseAgreement us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:FundsReceivedForStockPurchaseAgreement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-06-30	2021-03-31	2020-12-31
Value	0.0	200	0.0
Percentage of FundsReceivedForStockPurchaseAgreement	0.0	100.0	0.0

rcus:IncreaseDecreaseInAccruedResearchAndDevelopmentExpenses

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30
Value	5.733	4.716	-9.93	14	7.101	2.226	-1.233	-7.105
Percentage of IncreaseDecreaseInAccruedResearchAndDevelopmentExpenses	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:IncreaseDecreaseInDeferredRent

Period End	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	1007000.0	-137000.0	-129000.0	-141000.0	-135000.0	-135000.0	-127000.0	-124000.0	-120000.0	-139000.0	-85000.0	687000.0	-162000.0	-163000.0	-153000.0
Percentage of IncreaseDecreaseInDeferredRent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:IncreaseDecreaseInOperatingLeaseLiabilities

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	-398000.0	-605000.0	-287000.0	-273000.0
Percentage of IncreaseDecreaseInOperatingLeaseLiabilities	100.0	100.0	100.0	100.0

rcus:InterestAndOtherIncomeExpenseNonoperatingNet

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31
Value	166000.0	154000.0	159000.0	270000.0	301000.0	647000.0	929000.0	1254000.0	1482000.0	1534000.0	1512000.0	1519000.0	1288000.0	603000.0
Percentage of InterestAndOtherIncomeExpenseNonoperatingNet	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:MilestoneExpense us-gaap:CounterpartyName

rcus:MilestoneExpense

rcus:AbmunoLicenseAgreement

Period End	2021-06-30	2021-03-31	2020-09-30
Value	0	5000000.0	3000000.0
Percentage of MilestoneExpense	0.0	100.0	100.0

rcus:WuXiBiologicsLicenseAgreement

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30
Value	0	10000000.0	0	5000000.0
Percentage of MilestoneExpense	0.0	200.0	0.0	0.0

rcus:MilestonePayments us-gaap:CounterpartyName, us-gaap:IncomeStatementLocation, us-gaap:TypeOfArrangement

rcus:MilestonePayments

rcus:StrataOncologyInc, us-gaap:ResearchAndDevelopmentExpense, rcus:StrataAgreement

Period End	2021-06-30
Value	0
Percentage of MilestonePayments	0.0

rcus:NetExpensesOfInception us-gaap:CounterpartyName

rcus:NetExpensesOfInception

rcus:Genentech

Period End	2021-06-30	2021-03-31
Value	200000.0	800000.0
Percentage of NetExpensesOfInception	100.0	100.0

rcus:NonRefundableAndNonCreditableUpfrontCashPayments us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:NonRefundableAndNonCreditableUpfrontCashPayments

rcus:TaihoPharmaceuticalCoLtd, rcus:OptionAndLicenseAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2019-09-30	2019-06-30	2019-03-31
Value	0.0	35	0.0	0.0	0.0	35
Percentage of NonRefundableAndNonCreditableUpfrontCashPayments	0.0	100.0	0.0	0.0	0.0	100.0

rcus:OptionFeePerProgramForAllOtherProgramsEnteringClinicalDevelopmentToExerciseOption us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:OptionFeePerProgramForAllOtherProgramsEnteringClinicalDevelopmentToExerciseOption

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	150
Percentage of OptionFeePerProgramForAllOtherProgramsEnteringClinicalDevelopmentToExerciseOption	100.0

rcus:OptionFeePerProgramForCurrentClinicalProgramsToExerciseOption us-gaap:CounterpartyName, us-gaap:Range, us-gaap:SubsequentEventType, us-gaap:TypeOfArrangement

rcus:OptionFeePerProgramForCurrentClinicalProgramsToExerciseOption

rcus:GileadSciencesInc, srt:Maximum, us-gaap:SubsequentEvent, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	275
Percentage of OptionFeePerProgramForCurrentClinicalProgramsToExerciseOption	100.0

rcus:GileadSciencesInc, srt:Minimum, us-gaap:SubsequentEvent, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	200
Percentage of OptionFeePerProgramForCurrentClinicalProgramsToExerciseOption	72.7

rcus:OptionPaymentUponAchievementOfCertainDevelopmentMilestones us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:OptionPaymentUponAchievementOfCertainDevelopmentMilestones

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	250
Percentage of OptionPaymentUponAchievementOfCertainDevelopmentMilestones	100.0

rcus:PaymentForAccessRightsRelatedToTheCompanySResearch

Period End	2020-12-31
Value	0.874
Percentage of PaymentForAccessRightsRelatedToTheCompanySResearch	100.0

rcus:PercentageOfOptionToPurchaseMaximumSharesOfCommonStock us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:PercentageOfOptionToPurchaseMaximumSharesOfCommonStock

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	35.0
Percentage of PercentageOfOptionToPurchaseMaximumSharesOfCommonStock	100.0

rcus:PercentageOfPremiumPurchasePriceOfCommonStock us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:PercentageOfPremiumPurchasePriceOfCommonStock

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	20.0
Percentage of PercentageOfPremiumPurchasePriceOfCommonStock	100.0

rcus:PremiumFromStockPurchaseAgreement

Period End	2020-12-31
Value	0.0
Percentage of PremiumFromStockPurchaseAgreement	0.0

rcus:PremiumPaidOnStockPurchaseAgreement us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:PremiumPaidOnStockPurchaseAgreement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-06-30	2021-03-31	2020-12-31
Value	0.0	90	0.0
Percentage of PremiumPaidOnStockPurchaseAgreement	0.0	100.0	0.0

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	90
Percentage of PremiumPaidOnStockPurchaseAgreement	0.0

rcus:ProceedsFromIssuanceOfCommonStockToRelatedParty

Period End	2021-03-31
Value	220
Percentage of ProceedsFromIssuanceOfCommonStockToRelatedParty	100.0

rcus:ProceedsFromSaleOfShortTermAndLongTermInvestments

Period End	2021-06-30	2021-03-31
Value	0	7500000.0
Percentage of ProceedsFromSaleOfShortTermAndLongTermInvestments	0.0	100.0

rcus:ReceivableFromRelatedParty

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	-3600000.0	3981000.0	0	0
Percentage of ReceivableFromRelatedParty	100.0	100.0	0.0	0.0

rcus:ReimbursementOfMilestoneExpenseOfCostSharingProvisions us-gaap:RelatedPartyTransactionsByRelatedParty, us-gaap:TypeOfArrangement

rcus:ReimbursementOfMilestoneExpenseOfCostSharingProvisions

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31
Value	0	4000000.0
Percentage of ReimbursementOfMilestoneExpenseOfCostSharingProvisions	0.0	100.0

rcus:ReimbursementOfResearchAndDevelopmentExpenseExcludingAcquiredInProcessCosts us-gaap:TypeOfArrangement

rcus:ReimbursementOfResearchAndDevelopmentExpenseExcludingAcquiredInProcessCosts

rcus:DevelopmentAndCommercializationServices

Period End	2020-09-30
Value	500000.0
Percentage of ReimbursementOfResearchAndDevelopmentExpenseExcludingAcquiredInProcessCosts	100.0

rcus:RelatedPartyTransactionReimbursementFromRelatedPartyForSharedCosts us-gaap:IncomeStatementLocation

rcus:RelatedPartyTransactionReimbursementFromRelatedPartyForSharedCosts

us-gaap:ResearchAndDevelopmentExpense

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	-1176000.0	-4924000.0	0	0
Percentage of RelatedPartyTransactionReimbursementFromRelatedPartyForSharedCosts	100.0	100.0	0.0	0.0

rcus:RelatedPartyTransactionReimbursementFromRelatedPartyForSharedCosts us-gaap:IncomeStatementLocation, us-gaap:RelatedPartyTransactionsByRelatedParty

us-gaap:ResearchAndDevelopmentExpense, rcus:GileadSciencesInc

Period End	2021-06-30	2021-03-31
Value	1200000.0	4900000.0
Percentage of RelatedPartyTransactionReimbursementFromRelatedPartyForSharedCosts	-102.0	-99.5

rcus:RepurchaseOfUnvestedSharesOfStock

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	5000.0	16000.0	0	33000.0	0	43000.0	46000.0	5000.0	0	0	0
Percentage of RepurchaseOfUnvestedSharesOfStock	100.0	100.0	0.0	100.0	0.0	100.0	100.0	100.0	0.0	0.0	0.0

rcus:StockIssuedDuringPeriodValueDeterminedToPremiumOnPurchaseOfCommonStockAndAllocatedToPerformanceObligation us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:StockIssuedDuringPeriodValueDeterminedToPremiumOnPurchaseOfCommonStockAndAllocatedToPerformanceObligation

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	90
Percentage of StockIssuedDuringPeriodValueDeterminedToPremiumOnPurchaseOfCommonStockAndAllocatedToPerformanceObligation	100.0

rcus:StockIssuedDuringPeriodValueStockOptionsExercisedAndVestingOfRestrictedStock

Period End	2021-06-30	2021-03-31
Value	843000.0	1885000.0
Percentage of StockIssuedDuringPeriodValueStockOptionsExercisedAndVestingOfRestrictedStock	100.0	100.0

rcus:StockIssuedDuringPeriodValueStockOptionsExercisedAndVestingOfRestrictedStock us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2021-03-31
Value	843000.0	1885000.0
Percentage of StockIssuedDuringPeriodValueStockOptionsExercisedAndVestingOfRestrictedStock	100.0	100.0

rcus:StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOption

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	175000.0	183000.0	216000.0	220000.0
Percentage of StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOption	100.0	100.0	100.0	100.0

rcus:StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOption us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	175000.0	183000.0	216000.0	220000.0
Percentage of StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOption	100.0	100.0	100.0	100.0

rcus:StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptionsAndRestrictedStock

Period End	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	208000.0	216000.0	220000.0	252000.0	260000.0	273000.0	335000.0	387000.0	278000.0
Percentage of StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptionsAndRestrictedStock	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptionsAndRestrictedStock us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

Period End	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2019-03-31	2018-09-30	2018-06-30	2018-03-31
Value	208000.0	216000.0	220000.0	252000.0	260000.0	273000.0	335000.0	387000.0	278000.0
Percentage of StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptionsAndRestrictedStock	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:SubLicenseFeesIncurred us-gaap:CounterpartyName, us-gaap:IncomeStatementLocation

rcus:SubLicenseFeesIncurred

rcus:WuXiBiologicsLicenseAgreement, us-gaap:ResearchAndDevelopmentExpense

Period End	2021-06-30
Value	0.0
Percentage of SubLicenseFeesIncurred	0.0

rcus:SubLicenseFeesIncurred us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	10
Percentage of SubLicenseFeesIncurred	0.0

rcus:UnrealizedGainLossOnEquityMethodInvestments us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName

rcus:UnrealizedGainLossOnEquityMethodInvestments

rcus:PACTPharma

Period End	2021-06-30	2021-03-31	2020-12-31
Value	-800000.0	-800000.0	-100000.0
Percentage of UnrealizedGainLossOnEquityMethodInvestments	100.0	100.0	100.0

rcus:UpfrontAndMilestonePayments us-gaap:CounterpartyName

rcus:UpfrontAndMilestonePayments

rcus:AbmunoLicenseAgreement

Period End	2021-06-30	2021-03-31	2020-09-30	2020-06-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	0.0	14	9.6	0.0	0.0	0.0	0.0	2.0	0.0	0.8	0.0	0.0	0.0	3.8
Percentage of UpfrontAndMilestonePayments	0.0	100.0	100.0	0.0	0.0	0.0	0.0	100.0	0.0	100.0	0.0	0.0	0.0	100.0

rcus:UpfrontAndMilestonePayments us-gaap:CounterpartyName, us-gaap:IncomeStatementLocation

rcus:WuXiBiologicsLicenseAgreement, us-gaap:ResearchAndDevelopmentExpense

Period End	2021-06-30	2020-09-30	2020-06-30	2019-06-30
Value	0.0	5.0	0.0	7.5
Percentage of UpfrontAndMilestonePayments	0.0	52.1	0.0	0.0

rcus:UpfrontCashPayment

Period End	2020-12-31
Value	0.0
Percentage of UpfrontCashPayment	0.0

rcus:UpfrontCashPayment us-gaap:CounterpartyName, us-gaap:IncomeStatementLocation

rcus:WuXiBiologicsLicenseAgreement, us-gaap:ResearchAndDevelopmentExpense

Period End	2020-12-31
Value	0.5
Percentage of UpfrontCashPayment	0.0

rcus:UpfrontCashPayment us-gaap:CounterpartyName, us-gaap:SubsequentEventType, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, us-gaap:SubsequentEvent, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	175
Percentage of UpfrontCashPayment	0.0

rcus:UpfrontCashPayment us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-07-13
Value	0.0	175	0.0	175
Percentage of UpfrontCashPayment	0.0	0.0	0.0	0.0

rcus:VestingOfEarlyExercisedStockOptions

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	175000.0	183000.0	216000.0	220000.0
Percentage of VestingOfEarlyExercisedStockOptions	100.0	100.0	100.0	100.0

rcus:VestingOfEarlyExercisedStockOptionsAndRestrictedStock

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30
Value	205000.0	207000.0	216000.0	220000.0	245000.0	251000.0	260000.0	273000.0	294000.0	335000.0	369000.0	278000.0	95000.0	54000.0
Percentage of VestingOfEarlyExercisedStockOptionsAndRestrictedStock	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:ZimberelimabLicense

Period End	2020-12-31
Value	0.0
Percentage of ZimberelimabLicense	0.0

us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	-906000.0	-506000.0	-287000.0	10000.0	75000.0	248000.0	425000.0	633000.0	833000.0	747000.0	735000.0	1017000.0	0	0	82000.0
Percentage of AccretionAmortizationOfDiscountsAndPremiumsInvestments	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	0.0	0.0	100.0

us-gaap:AdjustmentForAmortization us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:AdjustmentForAmortization

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	100000.0	100000.0	-900000.0	1100000.0
Percentage of AdjustmentForAmortization	100.0	100.0	100.0	100.0

us-gaap:AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-03-31	2020-09-30
Value	0.055	1.931
Percentage of AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts	100.0	100.0

us-gaap:CapitalExpendituresIncurredButNotYetPaid

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	3704000.0	2784000.0	1338000.0	135000.0	34000.0	76000.0	-21000.0	-15000.0	-332000.0	380000.0	33000.0	-904000.0	312000.0	695000.0	315000.0	-472000.0	-605000.0	1100000.0
Percentage of CapitalExpendituresIncurredButNotYetPaid	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:ContractWithCustomerLiabilityRevenueRecognized us-gaap:RelatedPartyTransactionsByRelatedParty, us-gaap:TypeOfArrangement

us-gaap:ContractWithCustomerLiabilityRevenueRecognized

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	7.7	7.7	7.7	62
Percentage of ContractWithCustomerLiabilityRevenueRecognized	100.0	100.0	100.0	100.0

us-gaap:DeferredRevenueRevenueRecognized1

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31
Value	9.461	9.461	1.75	1.75	1.75	1.75	1.75	1.75	1.75	1.75
Percentage of DeferredRevenueRevenueRecognized1	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:DepreciationAndAmortization

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	820000.0	800000.0	778000.0	742000.0	787000.0	842000.0	856000.0	800000.0	800000.0	953000.0	947000.0	900000.0	900000.0	828000.0	766000.0	732000.0	628000.0	486000.0
Percentage of DepreciationAndAmortization	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:GainLossOnSaleOfEquityInvestments

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30
Value	0	0	131000.0	482000.0	0	0	0	0	0	0	1229000.0
Percentage of GainLossOnSaleOfEquityInvestments	0.0	0.0	100.0	100.0	0.0	0.0	0.0	0.0	0.0	0.0	100.0

us-gaap:GainLossOnSaleOfEquityInvestments us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName

rcus:PACTPharma

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31
Value	500000.0	1500000.0	200000.0	1300000.0
Percentage of GainLossOnSaleOfEquityInvestments	0.0	0.0	152.7	269.7

us-gaap:IncomeLossFromContinuingOperationsPerBasicAndDilutedShare

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-1.09	-1.08	-0.93	-0.63	-0.38	-0.51	-0.64	-0.41	-0.28	-0.25	-0.32	-1.37	-5.98	-11.86	-5.64	-4.96
Percentage of IncomeLossFromContinuingOperationsPerBasicAndDilutedShare	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:IncomeLossFromEquityMethodInvestments

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	0	0	-131000.0	-482000.0	0	-357000.0	-412000.0	-431000.0	-323000.0	-186000.0	-151000.0	-226000.0	-156000.0	-119000.0	-71000.0	-70000.0
Percentage of IncomeLossFromEquityMethodInvestments	0.0	0.0	100.0	100.0	0.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:IncomeLossFromEquityMethodInvestments us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName

rcus:PACTPharma

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	1200000.0	0	-100000.0	-500000.0	0	-400000.0	-400000.0	-400000.0	-300000.0	-200000.0	-200000.0	-200000.0	-100000.0	-70000.0	-70000.0	-70000.0
Percentage of IncomeLossFromEquityMethodInvestments	0.0	0.0	76.3	103.7	0.0	112.0	97.1	92.8	92.9	107.5	132.5	88.5	64.1	58.8	98.6	100.0

us-gaap:IncreaseDecreaseInAccruedLiabilities

Period End	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	1824000.0	13000.0	648000.0	-140000.0	-5890000.0	7923000.0	1606000.0	-644000.0	2329000.0	1402000.0	410000.0	971000.0	-210000.0	1290000.0	-469000.0
Percentage of IncreaseDecreaseInAccruedLiabilities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:IncreaseDecreaseInContractWithCustomerAsset

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-03-31	2018-12-31
Value	-3.66	4.186	-1.53	2.357	-0.122	0.212	-5.144	0.0	-5.0
Percentage of IncreaseDecreaseInContractWithCustomerAsset	100.0	100.0	100.0	100.0	100.0	100.0	100.0	0.0	100.0

us-gaap:IncreaseDecreaseInContractWithCustomerLiability

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31
Value	-9.461	-9.461	-9.511	191	-1.75	-1.75	-1.75	3.25	-1.75	-1.75	-1.562	3.709	-1.25	-1.25
Percentage of IncreaseDecreaseInContractWithCustomerLiability	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:IncreaseDecreaseInOtherAccruedLiabilities

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	2170000.0	-2007000.0	2239000.0	-1578000.0
Percentage of IncreaseDecreaseInOtherAccruedLiabilities	100.0	100.0	100.0	100.0

us-gaap:IncreaseDecreaseInOtherNoncurrentAssets

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31
Value	-408000.0	-63000.0	4001000.0	1238000.0	44000.0	91000.0	609000.0	-56000.0	5000.0	30000.0	80000.0	0	0	0
Percentage of IncreaseDecreaseInOtherNoncurrentAssets	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	0.0	0.0	0.0

us-gaap:IncreaseDecreaseInOtherNoncurrentLiabilities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	0.0	-0.002	2.228	7.663
Percentage of IncreaseDecreaseInOtherNoncurrentLiabilities	0.0	100.0	100.0	100.0

us-gaap:IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	4518000.0	4568000.0	-7047000.0	3284000.0	897000.0	3704000.0	80000.0	950000.0	193000.0	759000.0	-8000.0	779000.0	-284000.0	693000.0	-537000.0	922000.0	270000.0	96000.0
Percentage of IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:IncrementalCommonSharesAttributableToContingentlyIssuableShares

Period End	2020-09-30
Value	7588.0
Percentage of IncrementalCommonSharesAttributableToContingentlyIssuableShares	100.0

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements

Period End	2020-09-30
Value	2538900.0
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	100.0

us-gaap:OperatingLeaseCost

Period End	2021-06-30	2020-06-30
Value	1500000.0	500000.0
Percentage of OperatingLeaseCost	100.0	100.0

us-gaap:OperatingLeaseRightOfUseAssetAmortizationExpense

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	579000.0	538000.0	150000.0	144000.0
Percentage of OperatingLeaseRightOfUseAssetAmortizationExpense	100.0	100.0	100.0	100.0

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	-44000.0	-46000.0	-37000.0	-63000.0	-144000.0	224000.0	11000.0	-59000.0	84000.0	136000.0	1000.0	-25000.0	14000.0	-55000.0	-33000.0	14000.0	11000.0	-8000.0
Percentage of OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:ProceedsFromIssuanceOfCommonStock

Period End	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-03-31
Value	0.0	107	325	0.643	0.0
Percentage of ProceedsFromIssuanceOfCommonStock	0.0	100.0	100.0	100.0	0.0

us-gaap:ProceedsFromIssuanceOfCommonStock us-gaap:CounterpartyName, us-gaap:SubsequentEventType

rcus:GileadSciencesInc, us-gaap:SubsequentEvent

Period End	2021-02-24
Value	220
Percentage of ProceedsFromIssuanceOfCommonStock	0.0

us-gaap:ProceedsFromIssuanceOfCommonStock us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-01-31	2020-07-13
Value	220	107
Percentage of ProceedsFromIssuanceOfCommonStock	0.0	0.0

us-gaap:ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30
Value	2237000.0	1885000.0	1682000.0	270000.0	2358000.0	643000.0	520000.0	2000.0
Percentage of ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:ProceedsFromLinesOfCredit us-gaap:StatementGeographical, us-gaap:SubsequentEventType

us-gaap:ProceedsFromLinesOfCredit

stpr:CA, us-gaap:SubsequentEvent

Period End	2021-04-30
Value	1000000.0
Percentage of ProceedsFromLinesOfCredit	100.0

us-gaap:ProceedsFromSaleMaturityAndCollectionsOfInvestments

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	187	251	172	43	42	49	55	87	78	87	42	49	34	25	17
Percentage of ProceedsFromSaleMaturityAndCollectionsOfInvestments	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:RevenueFromRelatedParties

Period End	2021-06-30	2021-03-31	2020-06-30	2020-03-31
Value	7.711	7.711	0.0	0.0
Percentage of RevenueFromRelatedParties	100.0	100.0	0.0	0.0

us-gaap:ShortTermLeaseCost

Period End	2021-06-30
Value	100000.0
Percentage of ShortTermLeaseCost	100.0

us-gaap:StockIssuedDuringPeriodSharesNewIssues us-gaap:CounterpartyName, us-gaap:SubsequentEventType, us-gaap:TypeOfArrangement

us-gaap:StockIssuedDuringPeriodSharesNewIssues

rcus:GileadSciencesInc, us-gaap:SubsequentEvent, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	5.963029
Percentage of StockIssuedDuringPeriodSharesNewIssues	100.0

us-gaap:StockIssuedDuringPeriodValueEmployeeStockPurchasePlan

Period End	2021-06-30	2020-06-30	2019-06-30
Value	1394000.0	607000.0	596000.0
Percentage of StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	100.0	100.0	100.0

us-gaap:StockIssuedDuringPeriodValueEmployeeStockPurchasePlan us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

Period End	2021-06-30	2020-06-30	2019-06-30
Value	1394000.0	607000.0	596000.0
Percentage of StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	100.0	100.0	100.0

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised

Period End	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2018-03-31
Value	270000.0	1751000.0	643000.0	1000.0	99000.0	80000.0
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

Period End	2020-09-30	2020-06-30	2020-03-31	2019-09-30	2019-06-30	2018-03-31
Value	270000.0	1751000.0	643000.0	1000.0	99000.0	80000.0
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31	2017-09-30	2017-06-30	2017-03-31
Value	1348900.0	1394600.0	-32819.0	1533100.0	1596300.0	1670600.0	56476.0	1847900.0	1611900.0	1023500.0	-142030.0	1614100.0	1916700.0	2110100.0	-60493.0	2045700.0	2207100.0	2097600.0
Percentage of WeightedAverageNumberOfSharesCommonStockSubjectToRepurchaseOrCancellation	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:WeightedAverageNumberOfSharesIssuedBasic

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30
Value	71	68	2.902052	64	50	45	0.132313	45
Percentage of WeightedAverageNumberOfSharesIssuedBasic	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:AccruedResearchAndDevelopmentExpensesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	28	23	18	28	13	6.798	4.572	5.805	12	4.954	2.816	3.604	2.082	2.051	1.193
Percentage of AccruedResearchAndDevelopmentExpensesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:CashCashEquivalentsAndAvailableForSaleInvestments

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	805	884	735	785	462	157	188	196	224	243	259	265	277	290	175
Percentage of CashCashEquivalentsAndAvailableForSaleInvestments	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:ContingentMilestonePaymentsReceivable us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ContingentMilestonePaymentsReceivable

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	400
Percentage of ContingentMilestonePaymentsReceivable	100.0

rcus:ContractualObligationAdditionalPaymentDue us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ContractualObligationAdditionalPaymentDue

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	100
Percentage of ContractualObligationAdditionalPaymentDue	100.0

rcus:DeferredRevenueRelatedPartiesClassifiedCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2019-12-31
Value	67	67	67	0.0
Percentage of DeferredRevenueRelatedPartiesClassifiedCurrent	100.0	100.0	100.0	0.0

rcus:DeferredRevenueRelatedPartiesNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2019-12-31
Value	102	110	117	0.0
Percentage of DeferredRevenueRelatedPartiesNoncurrent	100.0	100.0	100.0	0.0

rcus:DeferredRevenueRelatedToResearchAndDevelopmentPipeline us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:DeferredRevenueRelatedToResearchAndDevelopmentPipeline

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31
Value	106	114	121
Percentage of DeferredRevenueRelatedToResearchAndDevelopmentPipeline	100.0	100.0	100.0

rcus:DeferredTaxAssetsLeaseLiability

Period End	2020-12-31	2019-12-31
Value	9068000.0	6052000.0
Percentage of DeferredTaxAssetsLeaseLiability	100.0	100.0

rcus:DeferredTaxAssetsLeasingArrangements

Period End	2020-12-31
Value	3831000.0
Percentage of DeferredTaxAssetsLeasingArrangements	100.0

rcus:DeferredTaxLiabilitiesRightOfUseAssets

Period End	2020-12-31
Value	2704000.0
Percentage of DeferredTaxLiabilitiesRightOfUseAssets	100.0

rcus:FutureDevelopmentAndPromotionCostsContractLiability us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:FutureDevelopmentAndPromotionCostsContractLiability

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-07-13
Value	9700000.0	9700000.0	9700000.0	9200000.0
Percentage of FutureDevelopmentAndPromotionCostsContractLiability	100.0	100.0	100.0	100.0

rcus:FutureDevelopmentAndPromotionCostsContractLiability us-gaap:RelatedPartyTransactionsByRelatedParty

rcus:GileadSciencesInc

Period End	2020-09-30
Value	9200000.0
Percentage of FutureDevelopmentAndPromotionCostsContractLiability	0.0

rcus:FutureDevelopmentAndPromotionCostsContractLiabilityCurrent us-gaap:BalanceSheetLocation, us-gaap:RelatedPartyTransactionsByRelatedParty

rcus:FutureDevelopmentAndPromotionCostsContractLiabilityCurrent

us-gaap:OtherCurrentLiabilities, rcus:GileadSciencesInc

Period End	2020-09-30
Value	1900000.0
Percentage of FutureDevelopmentAndPromotionCostsContractLiabilityCurrent	100.0

rcus:FutureDevelopmentAndPromotionCostsContractLiabilityCurrent us-gaap:CounterpartyName, us-gaap:BalanceSheetLocation, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, us-gaap:OtherCurrentLiabilities, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-09-30
Value	1900000.0
Percentage of FutureDevelopmentAndPromotionCostsContractLiabilityCurrent	100.0

rcus:FutureDevelopmentAndPromotionCostsContractLiabilityNoncurrent us-gaap:BalanceSheetLocation, us-gaap:RelatedPartyTransactionsByRelatedParty

rcus:FutureDevelopmentAndPromotionCostsContractLiabilityNoncurrent

us-gaap:OtherNoncurrentLiabilities, rcus:GileadSciencesInc

Period End	2020-09-30
Value	7300000.0
Percentage of FutureDevelopmentAndPromotionCostsContractLiabilityNoncurrent	100.0

rcus:FutureDevelopmentAndPromotionCostsContractLiabilityNoncurrent us-gaap:CounterpartyName, us-gaap:BalanceSheetLocation, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, us-gaap:OtherNoncurrentLiabilities, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-09-30
Value	7300000.0
Percentage of FutureDevelopmentAndPromotionCostsContractLiabilityNoncurrent	100.0

rcus:LesseeOperatingLeaseAllowanceForTenantImprovements

Period End	2020-12-31	2020-06-30
Value	12	1.0
Percentage of LesseeOperatingLeaseAllowanceForTenantImprovements	100.0	100.0

rcus:LesseeOperatingLeaseAllowanceForTenantImprovements us-gaap:StatementGeographical, us-gaap:SubsequentEventType

stpr:CA, us-gaap:SubsequentEvent

Period End	2021-04-30
Value	5.8
Percentage of LesseeOperatingLeaseAllowanceForTenantImprovements	0.0

rcus:LesseeOperatingLeaseCollateralAmount us-gaap:StatementGeographical, us-gaap:SubsequentEventType

rcus:LesseeOperatingLeaseCollateralAmount

stpr:CA, us-gaap:SubsequentEvent

Period End	2021-04-30
Value	1000000.0
Percentage of LesseeOperatingLeaseCollateralAmount	100.0

rcus:LesseeOperatingLeaseLiabilityPaymentsDueThereafter

Period End	2021-06-30	2020-12-31
Value	42	4.311
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueThereafter	100.0	100.0

rcus:LesseeOperatingLeaseLiabilityPaymentsDueYearSix

Period End	2020-12-31
Value	3340000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueYearSix	100.0

rcus:LesseeOperatingLeaseOptionToIncreaseAllowanceForTenantImprovements

Period End	2020-12-31
Value	5.5
Percentage of LesseeOperatingLeaseOptionToIncreaseAllowanceForTenantImprovements	100.0

rcus:LesseeOperatingLeaseOptionToIncreaseAllowanceForTenantImprovements us-gaap:StatementGeographical, us-gaap:SubsequentEventType

stpr:CA, us-gaap:SubsequentEvent

Period End	2021-04-30
Value	10
Percentage of LesseeOperatingLeaseOptionToIncreaseAllowanceForTenantImprovements	0.0

rcus:LesseeOperatingLeaseTenantImprovementAllowanceReceivable

Period End	2021-06-30
Value	11
Percentage of LesseeOperatingLeaseTenantImprovementAllowanceReceivable	100.0

rcus:OperatingLeaseLiabilityNetOfTenantImprovementAllowancesReceivable

Period End	2021-06-30
Value	40
Percentage of OperatingLeaseLiabilityNetOfTenantImprovementAllowancesReceivable	100.0

rcus:OperatingLossCarryForwardsWithNoExpirationDate us-gaap:IncomeTaxAuthority

rcus:OperatingLossCarryForwardsWithNoExpirationDate

us-gaap:DomesticCountry

Period End	2020-12-31
Value	205
Percentage of OperatingLossCarryForwardsWithNoExpirationDate	100.0

rcus:OtherAccruedLiabilities

Period End	2021-06-30	2021-03-31	2020-12-31	2019-12-31
Value	351000.0	341000.0	616000.0	196000.0
Percentage of OtherAccruedLiabilities	100.0	100.0	100.0	100.0

rcus:PercentageOfOutstandingCommonStockOwned us-gaap:RelatedPartyTransactionsByRelatedParty

rcus:PercentageOfOutstandingCommonStockOwned

rcus:GileadSciencesInc

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	19.4	19.5	13.0	13.0
Percentage of PercentageOfOutstandingCommonStockOwned	100.0	100.0	100.0	100.0

rcus:PresentValueOfResearchAndDevelopmentInformationAccessRightsPaymentRelatedToYearTwo us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:PresentValueOfResearchAndDevelopmentInformationAccessRightsPaymentRelatedToYearTwo

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	100
Percentage of PresentValueOfResearchAndDevelopmentInformationAccessRightsPaymentRelatedToYearTwo	100.0

rcus:RelatedPartiesContractLiabilitiesNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2019-12-31
Value	9703000.0	9703000.0	9703000.0	0
Percentage of RelatedPartiesContractLiabilitiesNoncurrent	100.0	100.0	100.0	0.0

rcus:ResearchAndDevelopmentInformationAccessRightsPaymentRelatedToYearTwo us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:ResearchAndDevelopmentInformationAccessRightsPaymentRelatedToYearTwo

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2020-07-13
Value	100
Percentage of ResearchAndDevelopmentInformationAccessRightsPaymentRelatedToYearTwo	100.0

rcus:TenantImprovementAllowanceExpectedToBeReceivedInLessThanOneYearNetOfCurrentPortionOfLeaseLiability

Period End	2021-06-30
Value	9140000.0
Percentage of TenantImprovementAllowanceExpectedToBeReceivedInLessThanOneYearNetOfCurrentPortionOfLeaseLiability	100.0

us-gaap:AccountsReceivableRelatedPartiesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2019-12-31
Value	1324000.0	4924000.0	943000.0	0
Percentage of AccountsReceivableRelatedPartiesCurrent	100.0	100.0	100.0	0.0

us-gaap:AccruedProfessionalFeesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	756000.0	67000.0	295000.0	632000.0	437000.0	323000.0	183000.0	281000.0	268000.0	519000.0	211000.0	116000.0	100000.0	616000.0	706000.0
Percentage of AccruedProfessionalFeesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

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

us-gaap:AssetsFairValueDisclosure

rcus:CorporateSecuritiesAndCommercialPaper, us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	358	310	262	195	53	34	67	51	60	91	110	117	86	62	52
Percentage of AssetsFairValueDisclosure	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:USGovernmentAgencyObligations, us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring

Period End	2020-12-31	2019-12-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	25	74	103	89	46	46	57
Percentage of AssetsFairValueDisclosure	9.5	110.2	93.8	76.0	54.1	74.1	109.8

us-gaap:MoneyMarketFunds, us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	310	362	146	181	273	67	45	64	64	39	45	58	104	182	66
Percentage of AssetsFairValueDisclosure	86.5	116.8	55.8	92.8	512.8	194.7	67.0	125.1	107.2	43.5	40.6	49.6	120.6	292.0	127.7

us-gaap:USGovernmentAgenciesDebtSecurities, us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring

Period End	2021-03-31	2020-12-31	2020-09-30	2020-06-30
Value	5.002	25	34	14
Percentage of AssetsFairValueDisclosure	1.6	9.5	17.9	28.1

us-gaap:USTreasurySecurities, us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2019-12-31
Value	135	206	301	373	121	74
Percentage of AssetsFairValueDisclosure	37.8	66.5	114.7	191.2	227.1	110.2

us-gaap:AssetsFairValueDisclosure us-gaap:FairValueByAssetClass, us-gaap:FairValueByMeasurementFrequency

rcus:CorporateSecuritiesAndCommercialPaper, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	358	310	262	195	53	34	67	51	60	91	110	117	86	62	52
Percentage of AssetsFairValueDisclosure	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

rcus:USGovernmentAgencyObligations, us-gaap:FairValueMeasurementsRecurring

Period End	2020-12-31	2019-12-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	25	74	103	89	46	46	57
Percentage of AssetsFairValueDisclosure	9.5	110.2	93.8	76.0	54.1	74.1	109.8

us-gaap:MoneyMarketFunds, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	310	362	146	181	273	67	45	64	64	39	45	58	104	182	66
Percentage of AssetsFairValueDisclosure	86.5	116.8	55.8	92.8	512.8	194.7	67.0	125.1	107.2	43.5	40.6	49.6	120.6	292.0	127.7

us-gaap:USGovernmentAgenciesDebtSecurities, us-gaap:FairValueMeasurementsRecurring

Period End	2021-03-31	2020-12-31	2020-09-30	2020-06-30
Value	5.002	25	34	14
Percentage of AssetsFairValueDisclosure	1.6	9.5	17.9	28.1

us-gaap:USTreasurySecurities, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2019-12-31
Value	135	206	301	373	121	74
Percentage of AssetsFairValueDisclosure	37.8	66.5	114.7	191.2	227.1	110.2

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

us-gaap:FairValueInputsLevel1, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	310	362	146	181	273	67	45	64	64	39	45	58	104	182	66
Percentage of AssetsFairValueDisclosure	86.5	116.8	55.8	92.8	512.8	194.7	67.0	125.1	107.2	43.5	40.6	49.6	120.6	292.0	127.7

us-gaap:FairValueInputsLevel2, us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	494	522	588	603	189	90	142	132	159	203	214	207	173	108	109
Percentage of AssetsFairValueDisclosure	137.8	168.1	224.2	309.1	355.3	261.9	210.2	256.4	265.2	221.0	193.8	176.0	200.4	174.1	209.8

us-gaap:AssetsFairValueDisclosure us-gaap:FairValueByMeasurementFrequency

us-gaap:FairValueMeasurementsRecurring

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	805	884	735	785	462	157	188	196	224	243	259	265	277	290	175
Percentage of AssetsFairValueDisclosure	224.3	284.8	280.0	401.9	868.0	456.6	277.2	381.5	372.3	264.5	234.5	225.6	321.0	466.1	337.4

us-gaap:AvailableForSaleSecurities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	805	884	735	785	462	157	188	196	224	243	259	265	277	290	175
Percentage of AvailableForSaleSecurities	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:AvailableForSaleSecurities us-gaap:InvestmentType

rcus:CorporateSecuritiesAndCommercialPaper

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	358	310	262	195	53	34	67	51	60	91	110	117	86	62	52
Percentage of AvailableForSaleSecurities	44.6	35.1	35.7	24.9	11.5	21.9	36.1	26.2	26.9	37.8	42.6	44.3	31.2	21.5	29.6

rcus:USGovernmentAgencyObligations

Period End	2020-12-31	2019-12-31	2018-12-31
Value	25	74	103
Percentage of AvailableForSaleSecurities	3.4	39.7	40.0

us-gaap:MoneyMarketFunds

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	310	362	146	181	273	67	45	64	64	39	45	58	104	182	66
Percentage of AvailableForSaleSecurities	38.6	41.0	19.9	23.1	59.1	42.6	24.2	32.8	28.8	16.4	17.3	22.0	37.6	62.6	37.8

us-gaap:USGovernmentAgenciesDebtSecurities

Period End	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	5.002	25	34	14	103	89	46	46	57
Percentage of AvailableForSaleSecurities	0.6	3.4	4.5	3.2	40.0	33.7	16.8	15.9	32.5

us-gaap:USTreasurySecurities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2019-12-31
Value	135	206	301	373	121	74
Percentage of AvailableForSaleSecurities	16.9	23.3	41.0	47.6	26.2	39.7

us-gaap:AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31
Value	50000.0	56000.0	57000.0	87000.0	151000.0	315000.0	67000.0	54000.0	111000.0	32000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax us-gaap:InvestmentType

rcus:CorporateSecuritiesAndCommercialPaper

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30
Value	39000.0	14000.0	15000.0	27000.0	30000.0	9000.0	55000.0	12000.0	27000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	78.0	25.0	26.3	31.0	19.9	2.9	82.1	22.2	24.3

rcus:USGovernmentAgencyObligations

Period End	2020-12-31	2019-12-31
Value	4000.0	12000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	7.0	17.9

us-gaap:USGovernmentAgenciesDebtSecurities

Period End	2021-03-31	2020-12-31	2020-09-30
Value	2000.0	4000.0	6000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	3.6	7.0	6.9

us-gaap:USTreasurySecurities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2019-12-31
Value	11000.0	40000.0	38000.0	54000.0	121000.0	12000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	22.0	71.4	66.7	62.1	80.1	17.9

us-gaap:AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	96000.0	58000.0	13000.0	6000.0	7000.0	27000.0	3000.0	3000.0	108000.0	110000.0	84000.0	97000.0	42000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax us-gaap:InvestmentType

rcus:CorporateSecuritiesAndCommercialPaper

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	57000.0	56000.0	12000.0	5000.0	6000.0	27000.0	2000.0	3000.0	91000.0	67000.0	60000.0	54000.0	12000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	59.4	96.6	92.3	83.3	85.7	100.0	66.7	100.0	84.3	60.9	71.4	55.7	28.6

us-gaap:USTreasurySecurities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2019-12-31
Value	39000.0	2000.0	1000.0	1000.0	1000.0
Percentage of AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	40.6	3.4	7.7	16.7	33.3

us-gaap:AvailableForSaleSecuritiesAmortizedCost

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	805	884	735	785	462	157	188	196	224	243	259	265	277	290	175
Percentage of AvailableForSaleSecuritiesAmortizedCost	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:AvailableForSaleSecuritiesAmortizedCost us-gaap:InvestmentType

rcus:CorporateSecuritiesAndCommercialPaper

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	358	310	262	195	53	34	67	51	60	91	110	117	86	62	52
Percentage of AvailableForSaleSecuritiesAmortizedCost	44.6	35.1	35.7	24.9	11.5	22.0	36.1	26.2	26.9	37.8	42.7	44.3	31.2	21.5	29.6

rcus:USGovernmentAgencyObligations

Period End	2020-12-31	2019-12-31	2018-12-31
Value	24	74	103
Percentage of AvailableForSaleSecuritiesAmortizedCost	3.4	39.7	40.0

us-gaap:MoneyMarketFunds

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	310	362	146	181	273	67	45	64	64	39	45	58	104	182	66
Percentage of AvailableForSaleSecuritiesAmortizedCost	38.6	41.0	19.9	23.1	59.1	42.7	24.2	32.8	28.8	16.4	17.3	22.0	37.6	62.6	37.8

us-gaap:USGovernmentAgenciesDebtSecurities

Period End	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	5.0	24	34	14	103	89	46	46	57
Percentage of AvailableForSaleSecuritiesAmortizedCost	0.6	3.4	4.5	3.2	40.0	33.7	16.9	15.9	32.5

us-gaap:USTreasurySecurities

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2019-12-31
Value	135	206	301	373	120	74
Percentage of AvailableForSaleSecuritiesAmortizedCost	16.9	23.3	41.0	47.6	26.1	39.7

us-gaap:AvailableForSaleSecuritiesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	400	436	555	560	177	90	130	111	148	173	185	182	95	82	77
Percentage of AvailableForSaleSecuritiesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:AvailableForSaleSecuritiesDebtSecuritiesNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	84	57	6.44	2.7
Percentage of AvailableForSaleSecuritiesDebtSecuritiesNoncurrent	100.0	100.0	100.0	100.0

us-gaap:AvailableForSaleSecuritiesNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2019-09-30	2019-06-30	2019-03-31	2018-12-31
Value	84	57	6.44	2.7	5.992	0.0	1.201	3.181
Percentage of AvailableForSaleSecuritiesNoncurrent	100.0	100.0	100.0	100.0	100.0	0.0	100.0	100.0

us-gaap:CashAndCashEquivalentsFairValueDisclosure

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	320	390	173	221	285	67	57	78	76	68	71	74	169	198	98
Percentage of CashAndCashEquivalentsFairValueDisclosure	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	323	392	173	222	285	67	58	79	76	68	71	75	170	198	98
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:ContractWithCustomerAssetNet us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:ContractWithCustomerAssetNet

rcus:GileadSciencesInc, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	4000000.0	4100000.0	4200000.0	4300000.0
Percentage of ContractWithCustomerAssetNet	100.0	100.0	100.0	100.0

us-gaap:ContractWithCustomerAssetNetCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2018-12-31
Value	1575000.0	5235000.0	1049000.0	2579000.0	222000.0	344000.0	132000.0	5276000.0	0
Percentage of ContractWithCustomerAssetNetCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	0.0

us-gaap:ContractWithCustomerAssetNetCurrent us-gaap:CounterpartyName, us-gaap:BalanceSheetLocation, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, us-gaap:PrepaidExpensesAndOtherCurrentAssets, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-07-13
Value	1000000.0	1000000.0	1000000.0	2900000.0
Percentage of ContractWithCustomerAssetNetCurrent	63.5	19.1	95.3	0.0

us-gaap:ContractWithCustomerAssetNetCurrent us-gaap:RelatedPartyTransactionsByRelatedParty

rcus:GileadSciencesInc

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	1300000.0	4900000.0	900000.0	2500000.0
Percentage of ContractWithCustomerAssetNetCurrent	82.5	93.6	85.8	96.9

us-gaap:ContractWithCustomerAssetNetNoncurrent us-gaap:CounterpartyName, us-gaap:BalanceSheetLocation, us-gaap:TypeOfArrangement

us-gaap:ContractWithCustomerAssetNetNoncurrent

rcus:GileadSciencesInc, us-gaap:OtherNoncurrentAssets, rcus:OptionLicenseAndCollaborationAgreement

Period End	2021-06-30	2021-03-31	2020-12-31	2020-07-13
Value	3000000.0	3100000.0	3200000.0	1400000.0
Percentage of ContractWithCustomerAssetNetNoncurrent	100.0	100.0	100.0	100.0

us-gaap:ContractWithCustomerLiability us-gaap:RelatedPartyTransactionsByRelatedParty

us-gaap:ContractWithCustomerLiability

rcus:GileadSciencesInc

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	170	177	185	193
Percentage of ContractWithCustomerLiability	100.0	100.0	100.0	100.0

us-gaap:ContractWithCustomerLiabilityNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31
Value	103	113	122	91	8.522	10	12	13	10	12
Percentage of ContractWithCustomerLiabilityNoncurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:ContractWithCustomerLiabilityNoncurrent us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:TaihoPharmaceuticalCoLtd, rcus:OptionAndLicenseAgreement

Period End	2020-12-31	2019-12-31
Value	5.0	12
Percentage of ContractWithCustomerLiabilityNoncurrent	4.1	99.8

us-gaap:ContractWithCustomerLiabilityNoncurrent us-gaap:RelatedPartyTransactionsByRelatedParty

rcus:GileadSciencesInc

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30
Value	102	110	117	84
Percentage of ContractWithCustomerLiabilityNoncurrent	98.5	97.1	95.9	92.6

us-gaap:DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent us-gaap:PlanName

us-gaap:DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent

rcus:TwoThousandFifteenStockPlan

Period End	2020-12-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	700000.0	1700000.0	2000000.0	2300000.0	2600000.0	2800000.0	3100000.0	3500000.0	3800000.0	900000.0
Percentage of DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:DeferredIncomeTaxLiabilities

Period End	2020-12-31
Value	2704000.0
Percentage of DeferredIncomeTaxLiabilities	100.0

us-gaap:DeferredOfferingCosts us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:DeferredOfferingCosts

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	1900000.0
Percentage of DeferredOfferingCosts	100.0

us-gaap:DeferredRentCreditNoncurrent

Period End	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	4311000.0	3439000.0	3590000.0	3734000.0	3875000.0	4010000.0	4145000.0	4272000.0	4396000.0	4516000.0	4655000.0	4740000.0
Percentage of DeferredRentCreditNoncurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:DeferredTaxAssetsDeferredIncome

Period End	2020-12-31	2019-12-31	2018-12-31
Value	2407000.0	3277000.0	3909000.0
Percentage of DeferredTaxAssetsDeferredIncome	100.0	100.0	100.0

us-gaap:DeferredTaxAssetsGross

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31
Value	86	50	30	18
Percentage of DeferredTaxAssetsGross	100.0	100.0	100.0	100.0

us-gaap:DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31
Value	54	30	16	11
Percentage of DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal	100.0	100.0	100.0	100.0

us-gaap:DeferredTaxAssetsOther

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31
Value	5890000.0	2965000.0	1724000.0	1292000.0
Percentage of DeferredTaxAssetsOther	100.0	100.0	100.0	100.0

us-gaap:DeferredTaxAssetsTaxCreditCarryforwardsResearch

Period End	2020-12-31	2019-12-31	2018-12-31	2017-12-31
Value	11	8.077	5.087	2.706
Percentage of DeferredTaxAssetsTaxCreditCarryforwardsResearch	100.0	100.0	100.0	100.0

us-gaap:EmployeeRelatedLiabilitiesCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	8599000.0	7128000.0	8632000.0	6247000.0	3980000.0	2566000.0	4571000.0	3455000.0	2301000.0	1963000.0	2833000.0	2761000.0	1902000.0	643000.0	1026000.0
Percentage of EmployeeRelatedLiabilitiesCurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized us-gaap:AwardType

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized

us-gaap:EmployeeStockOption

Period End	2020-12-31
Value	88
Percentage of EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	100.0

us-gaap:RestrictedStockUnitsRSU

Period End	2020-12-31
Value	88
Percentage of EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	100.0

us-gaap:EquityMethodInvestmentOwnershipPercentage us-gaap:CounterpartyName, us-gaap:SubsequentEventType

us-gaap:EquityMethodInvestmentOwnershipPercentage

rcus:GileadSciencesInc, us-gaap:SubsequentEvent

Period End	2021-02-24
Value	19.5
Percentage of EquityMethodInvestmentOwnershipPercentage	100.0

us-gaap:InterestReceivableCurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2019-12-31
Value	1400000.0	1029000.0	649000.0	372000.0	239000.0	251000.0
Percentage of InterestReceivableCurrent	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:InvestmentsAndCash us-gaap:BalanceSheetLocation

us-gaap:InvestmentsAndCash

rcus:CashCashEquivalentsAndInvestmentsInMarketableSecurities

Period End	2021-06-30	2021-03-31	2020-09-30
Value	805	884	785
Percentage of InvestmentsAndCash	100.0	100.0	100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths

Period End	2021-06-30
Value	5722000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	100.0

us-gaap:LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear

Period End	2021-06-30
Value	2233000.0
Percentage of LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear	100.0

us-gaap:LineOfCredit us-gaap:CreditFacility

us-gaap:LineOfCredit

us-gaap:StandbyLettersOfCredit

Period End	2021-06-30	2021-03-31
Value	3000000.0	2000000.0
Percentage of LineOfCredit	100.0	100.0

us-gaap:OperatingLeaseWeightedAverageDiscountRatePercent

Period End	2021-06-30	2020-12-31
Value	5.2	7.3
Percentage of OperatingLeaseWeightedAverageDiscountRatePercent	100.0	100.0

us-gaap:OperatingLeasesFutureMinimumPaymentsDue

Period End	2020-12-31	2020-06-30	2019-12-31
Value	90	10	13
Percentage of OperatingLeasesFutureMinimumPaymentsDue	100.0	100.0	100.0

us-gaap:OperatingLossCarryforwards

Period End	2020-12-31	2019-12-31	2018-12-31
Value	253	137	70
Percentage of OperatingLossCarryforwards	100.0	100.0	100.0

us-gaap:OperatingLossCarryforwards us-gaap:IncomeTaxAuthority

us-gaap:StateAndLocalJurisdiction

Period End	2020-12-31	2019-12-31	2018-12-31
Value	15	16	15
Percentage of OperatingLossCarryforwards	6.3	12.3	21.7

us-gaap:RestrictedCashNoncurrent

Period End	2021-06-30	2021-03-31	2020-12-31	2020-09-30	2020-06-30	2020-03-31	2019-12-31	2019-09-30	2019-06-30	2019-03-31	2018-12-31	2018-09-30	2018-06-30	2018-03-31	2017-12-31
Value	3005000.0	1988000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0	203000.0
Percentage of RestrictedCashNoncurrent	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0

us-gaap:RestrictedCashNoncurrent us-gaap:CreditFacility

us-gaap:StandbyLettersOfCredit

Period End	2021-06-30	2021-03-31
Value	3000000.0	2000000.0
Percentage of RestrictedCashNoncurrent	99.8	100.6

us-gaap:SecurityDeposit

Period End	2021-06-30	2020-12-31
Value	3000000.0	200000.0
Percentage of SecurityDeposit	100.0	100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue us-gaap:AwardType, us-gaap:PlanName

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue

us-gaap:RestrictedStockUnitsRSU, rcus:TwoThousandEighteenEquityIncentivePlan

Period End	2020-12-31
Value	27.84
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice

Period End	2020-12-31
Value	10.28
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue

Period End	2020-12-31
Value	122
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue

Period End	2020-12-31
Value	122
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue	100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice

Period End	2020-12-31
Value	13.88
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice	100.0

us-gaap:SharePrice us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:SharePrice

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	33.54
Percentage of SharePrice	100.0

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1

Period End	2020-12-31
Value	44
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	100.0

us-gaap:SharesIssuedPricePerShare us-gaap:CounterpartyName, us-gaap:SubsequentEventType, us-gaap:TypeOfArrangement

us-gaap:SharesIssuedPricePerShare

rcus:GileadSciencesInc, us-gaap:SubsequentEvent, rcus:CommonStockPurchaseAgreement

Period End	2020-07-13
Value	33.54
Percentage of SharesIssuedPricePerShare	100.0

us-gaap:SharesIssuedPricePerShare us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-02-28	2021-01-31	2020-07-13
Value	39.0	39.0	33.54
Percentage of SharesIssuedPricePerShare	0.0	0.0	100.0

us-gaap:SharesIssuedPricePerShare us-gaap:RelatedPartyTransactionsByRelatedParty, us-gaap:TypeOfArrangement

rcus:GileadSciencesInc, rcus:CommonStockPurchaseAgreement

Period End	2021-02-28
Value	39.0
Percentage of SharesIssuedPricePerShare	0.0

us-gaap:TaxCreditCarryforwardAmount us-gaap:IncomeTaxAuthority, us-gaap:TaxCreditCarryforward

us-gaap:TaxCreditCarryforwardAmount

us-gaap:DomesticCountry, us-gaap:Research

Period End	2020-12-31	2019-12-31	2018-12-31
Value	9900000.0	6100000.0	3600000.0
Percentage of TaxCreditCarryforwardAmount	100.0	100.0	100.0

us-gaap:StateAndLocalJurisdiction, us-gaap:Research

Period End	2020-12-31	2019-12-31	2018-12-31
Value	5100000.0	5000000.0	3100000.0
Percentage of TaxCreditCarryforwardAmount	51.5	82.0	86.1

Line plots across dimensions of each concept

TTM Greenblatt ROC
_
(None,)

us-gaap:AllocatedShareBasedCompensationExpense
us-gaap:IncomeStatementLocation
(None,)

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax
us-gaap:ProductOrService
(None,)

us-gaap:Revenues
us-gaap:CounterpartyName, us-gaap:ProductOrService
('rcus:GileadSciencesIncAndTaihoPharmaceuticalCo', None)

us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents
(None,)

us-gaap:PropertyPlantAndEquipmentGross
us-gaap:PropertyPlantAndEquipmentByType
(None,)

us-gaap:StockholdersEquity
us-gaap:StatementEquityComponents
(None,)

RCUS

Table of contents

Plots across concepts

Tables

Common Stock Value

us-gaap:CommonStockValue

us-gaap:CommonStockValue

Weighted Average Number Of Diluted Shares Outstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

Weighted Average Number Of Shares Outstanding Basic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

Weighted Average Number Of Share Outstanding Basic And Diluted

us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted

us-gaap:WeightedAverageNumberOfShareOutstandingBasicAndDiluted

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareBasic

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted

us-gaap:EarningsPerShareDiluted

Earnings Per Share Basic And Diluted

us-gaap:EarningsPerShareBasicAndDiluted

us-gaap:EarningsPerShareBasicAndDiluted

Income Loss From Continuing Operations Per Basic Share

us-gaap:IncomeLossFromContinuingOperationsPerBasicShare

us-gaap:IncomeLossFromContinuingOperationsPerBasicShare

Income Loss From Continuing Operations Per Diluted Share

us-gaap:IncomeLossFromContinuingOperationsPerDilutedShare

us-gaap:IncomeLossFromContinuingOperationsPerDilutedShare

Allocated Share Based Compensation Expense

us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:AllocatedShareBasedCompensationExpense us-gaap:IncomeStatementLocation

us-gaap:GeneralAndAdministrativeExpense

us-gaap:ResearchAndDevelopmentExpense

Comprehensive Income Net Of Tax

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTax

General And Administrative Expense

us-gaap:GeneralAndAdministrativeExpense

us-gaap:GeneralAndAdministrativeExpense

Net Income Loss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings

Nonoperating Income Expense

us-gaap:NonoperatingIncomeExpense

us-gaap:NonoperatingIncomeExpense

Operating Expenses

us-gaap:OperatingExpenses

us-gaap:OperatingExpenses

Operating Income Loss

us-gaap:OperatingIncomeLoss

us-gaap:OperatingIncomeLoss

Other Comprehensive Income Loss Net Of Tax

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome

Profit Loss

us-gaap:ProfitLoss

us-gaap:ProfitLoss

Research And Development Expense

us-gaap:ResearchAndDevelopmentExpense

us-gaap:ResearchAndDevelopmentExpense

us-gaap:ResearchAndDevelopmentExpense us-gaap:CounterpartyName

rcus:Genentech

Research And Development Expense Excluding Acquired In Process Cost

us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost us-gaap:CounterpartyName, us-gaap:TypeOfArrangement

us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost

rcus:StrataOncologyInc, rcus:StrataAgreement

us-gaap:ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost us-gaap:TypeOfArrangement

rcus:AstraZenecaAgreement

Revenue From Contract With Customer Excluding Assessed Tax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:ProductOrService