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FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Dec. 31, 2013
Fair value disclosure        
Cash and cash equivalents $ 166,022,000us-gaap_CashAndCashEquivalentsAtCarryingValue $ 157,042,000us-gaap_CashAndCashEquivalentsAtCarryingValue $ 95,728,000us-gaap_CashAndCashEquivalentsAtCarryingValue $ 105,354,000us-gaap_CashAndCashEquivalentsAtCarryingValue
Short-term investments 45,980,000us-gaap_ShortTermInvestments 45,909,000us-gaap_ShortTermInvestments    
Restricted cash 1,386,000us-gaap_RestrictedCashAndInvestmentsCurrent 1,386,000us-gaap_RestrictedCashAndInvestmentsCurrent    
Concentrations of Credit Risk of Financial Instruments        
Cash and cash equivalents which are not FDIC-insured 84,700,000arcb_DepositsUninsuredAmount 77,300,000arcb_DepositsUninsuredAmount    
Fair value disclosure        
Fair value disclosure        
Cash and cash equivalents 166,022,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
157,042,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Fair value disclosure | Cash deposits        
Fair value disclosure        
Cash and cash equivalents 103,579,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_CashMember
99,615,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_CashMember
   
Restricted cash 1,386,000us-gaap_RestrictedCashAndInvestmentsCurrent
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_CashMember
1,386,000us-gaap_RestrictedCashAndInvestmentsCurrent
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_CashMember
   
Fair value disclosure | Variable rate demand notes        
Fair value disclosure        
Cash and cash equivalents 16,342,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_VariableRateDemandObligationMember
16,326,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_VariableRateDemandObligationMember
   
Fair value disclosure | Money market funds        
Fair value disclosure        
Cash and cash equivalents 46,101,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
41,101,000us-gaap_CashAndCashEquivalentsAtCarryingValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
   
Fair value disclosure | Certificates of deposit        
Fair value disclosure        
Short-term investments $ 45,980,000us-gaap_ShortTermInvestments
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember
$ 45,909,000us-gaap_ShortTermInvestments
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_CertificatesOfDepositMember