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EMPLOYEE BENEFIT PLANS (Details 2) (USD $) | 12 Months Ended | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | 2 Months Ended | 10 Months Ended | 12 Months Ended |
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Dec. 31, 2014 | Dec. 31, 2013 | Jan. 31, 2014 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Dec. 31, 2012 | Dec. 31, 2014 | Oct. 31, 2014 | Dec. 31, 2011 | Jan. 01, 2014
Distributions and pension settlement expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pension settlement expense, pre-tax | $ 6,595,000 us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1 | $ 2,111,000 us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1 |  |  |  |  |  |  |  |  |  |  |  |  |
Nonunion Defined Benefit Pension Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributions and pension settlement expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pension settlement distributions | 57,518,000 us-gaap_DefinedBenefitPlanSettlementsPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 20,104,000 us-gaap_DefinedBenefitPlanSettlementsPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |
Pension settlement expense, pre-tax | 5,880,000 us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 2,111,000 us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |
Pension settlement expense per diluted share, net of taxes | $ 0.14 arcb_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsPerDilutedShareNetOfTaxes / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | $ 0.05 arcb_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsPerDilutedShareNetOfTaxes / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |
Premium paid to purchase nonparticipating annuity contract | 25,400,000 arcb_NonparticipatingAnnuityContractPremiumPaid / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 25,400,000 arcb_NonparticipatingAnnuityContractPremiumPaid / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |
Lump-sum distributions | 32,100,000 arcb_DefinedBenefitPlanLumpSumDistributionPaid / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax amounts included in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized net actuarial loss | 24,303,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 16,003,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 24,303,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  | 16,003,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  | 24,303,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Total | 24,303,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 16,003,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 24,303,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  | 16,003,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  | 24,303,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Pre-tax amounts, which are reported within accumulated other comprehensive loss, expected to be recognized as components of net periodic benefit cost in next fiscal year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized net actuarial loss | 3,008,000 us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | 3,008,000 us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted-average assumptions used to determine nonunion benefit obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (as a percent) | 3.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 3.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  | 3.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  | 3.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Weighted-average assumptions used to determine net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (as a percent) |  |  |  | 3.40%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.30%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.90%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.10%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 3.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |
Expected return on plan assets (as a percent) | 6.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  | 7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |
Rate of compensation increase (as a percent) |  | 3.30%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  |  | 3.30%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |
Estimated future benefit payments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 | 31,108,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  | 31,108,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  | 31,108,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
2016 | 14,813,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  | 14,813,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  | 14,813,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
2017 | 14,341,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  | 14,341,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  | 14,341,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
2018 | 13,622,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  | 13,622,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  | 13,622,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
2019 | 13,408,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  | 13,408,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  | 13,408,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
2020-2024 | 55,806,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  | 55,806,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |  |  |  |  |  | 55,806,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Required minimum contributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Adjusted funding target attainment percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 112.30%arcb_DefinedBenefitPlanFundingTargetAttainmentPercentage / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Supplemental Benefit Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distributions and pension settlement expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pension settlement distributions | 853,000 us-gaap_DefinedBenefitPlanSettlementsPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  |  |  | 1,126,000 us-gaap_DefinedBenefitPlanSettlementsPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |
Pension settlement expense, pre-tax | 715,000 us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pension settlement expense per diluted share, net of taxes | $ 0.02 arcb_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsPerDilutedShareNetOfTaxes / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of delay for pension settlement distribution to key employees | 6 months |  |  |  |  |  |  |  |  |  |  |  |  | 6 months |
Pre-tax amounts included in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized net actuarial loss | 1,207,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 1,778,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  | 1,207,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  | 1,778,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  | 1,207,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |
Total | 1,207,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 1,778,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  | 1,207,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  | 1,778,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  | 1,207,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |
Pre-tax amounts, which are reported within accumulated other comprehensive loss, expected to be recognized as components of net periodic benefit cost in next fiscal year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized net actuarial loss | 159,000 us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | 159,000 us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted-average assumptions used to determine nonunion benefit obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (as a percent) | 2.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 2.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  | 2.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  | 2.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  | 2.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |
Weighted-average assumptions used to determine net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (as a percent) |  | 2.10%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  |  | 3.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 2.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 2.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |
Estimated future benefit payments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 | 1,941,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  | 1,941,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  | 1,941,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |
2016 | 1,235,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  | 1,235,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  | 1,235,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |
2019 | 3,107,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  | 3,107,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |  |  |  |  |  | 3,107,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |  |  |
Postretirement Health Benefit Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax amounts included in accumulated other comprehensive loss that have not yet been recognized in net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized net actuarial loss | 5,327,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember | 150,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  | 5,327,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | 150,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | 5,327,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
Unrecognized prior service credit | (697,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember | (887,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  | (697,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | (887,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | (697,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
Total | 4,630,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember | (737,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  | 4,630,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | (737,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | 4,630,000 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
Pre-tax amounts, which are reported within accumulated other comprehensive loss, expected to be recognized as components of net periodic benefit cost in next fiscal year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized net actuarial loss | 622,000 us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized prior service credit | (190,000)us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | 432,000 us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted-average assumptions used to determine nonunion benefit obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (as a percent) | 3.90%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember | 4.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  | 3.90%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | 4.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  | 3.90%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
Weighted-average assumptions used to determine net periodic benefit cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (as a percent) | 4.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember | 3.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  | 4.30%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |
Effects of one-percentage-point change in assumed health care cost trend rates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effect of one-percentage-point increase on total of service and interest cost components | 204,000 us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effect of one-percentage-point decrease on total of service and interest cost components | (164,000)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effect of one-percentage-point increase on postretirement benefit obligation | 4,321,000 us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effect of one-percentage-point decrease on postretirement benefit obligation | (3,450,000)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated future benefit payments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 | 684,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  | 684,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  | 684,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
2016 | 750,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  | 750,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  | 750,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
2017 | 813,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  | 813,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  | 813,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
2018 | 916,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  | 916,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  | 916,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
2019 | 963,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  | 963,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  | 963,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
2020-2024 | $ 5,509,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  | $ 5,509,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |  |  |  |  |  | $ 5,509,000 us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember |  |  |
Postretirement Health Benefit Plan | Pre-65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assumed health care cost trend rates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Health care cost trend rate assumed for next year (as a percent) | 7.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsUnderAge65Member | 8.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsUnderAge65Member |  |  |  |  |  |  |  |  |  |  |  |  |
Rate to which the cost trend rate is assumed to decline (as a percent) | 4.50%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsUnderAge65Member | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsUnderAge65Member |  |  |  |  |  |  |  |  |  |  |  |  |
Year that the rate reaches the cost trend assumed rate | 2027 | 2020 |  | 2027 |  |  |  | 2020 |  |  |  | 2027 |  |  |
Postretirement Health Benefit Plan | Post-65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assumed health care cost trend rates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Health care cost trend rate assumed for next year (as a percent) | 5.80%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsAge65AndOlderMember | 5.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsAge65AndOlderMember |  |  |  |  |  |  |  |  |  |  |  |  |
Rate to which the cost trend rate is assumed to decline (as a percent) | 4.50%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsAge65AndOlderMember | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_TitleOfIndividualAxis = arcb_PlanParticipantsAge65AndOlderMember |  |  |  |  |  |  |  |  |  |  |  |  |
Year that the rate reaches the cost trend assumed rate | 2020 | 2020 |  | 2020 |  |  |  | 2020 |  |  |  | 2020 |  |  |

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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The interest rate used to adjust for the time value of money for the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The interest rate used to adjust for the time value of money. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Glossary Expected Long-Term Rate of Return on Plan Assets -URI http://asc.fasb.org/extlink&oid=6512013 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Expected rate of compensation increases (for pay-related plans). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of benefits from a defined benefit plan expected to be paid in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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- Definition Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 + Details
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- Definition Amount of net gain (loss) recognized in net periodic benefit cost as a result of an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include, but are not limited to, lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contracts to cover vested benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 15 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(7) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The amount that relates to an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include (a) making lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and (b) purchasing nonparticipating annuity contracts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 15 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(8) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The ultimate trend rate for health care costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Year the ultimate health care cost trend rate is expected to be reached, in CCYY format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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