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Share-Based Compensation - Valuation Techniques (Details) (Monte Carlo Simulation, Fair Value, Measurements, Recurring, Share Based Compensation Liability, USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Monte Carlo Simulation | Fair Value, Measurements, Recurring | Share Based Compensation Liability
    
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
OPP $ 23,400arct_ShareBasedCompensationFairValueLiability
/ us-gaap_FairValueByLiabilityClassAxis
= arct_ShareBasedCompensationLiabilityMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_ValuationTechniqueAxis
= arct_MonteCarloSimulationMember		 $ 29,100arct_ShareBasedCompensationFairValueLiability
/ us-gaap_FairValueByLiabilityClassAxis
= arct_ShareBasedCompensationLiabilityMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_ValuationTechniqueAxis
= arct_MonteCarloSimulationMember
Expected volatility 24.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_FairValueByLiabilityClassAxis
= arct_ShareBasedCompensationLiabilityMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_ValuationTechniqueAxis
= arct_MonteCarloSimulationMember		 27.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_FairValueByLiabilityClassAxis
= arct_ShareBasedCompensationLiabilityMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_ValuationTechniqueAxis
= arct_MonteCarloSimulationMember