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PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Multiemployer Plans) (Details) $ in Thousands |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Aug. 01, 2018 | Jun. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) plan | Dec. 31, 2017
Multiemployer Plans |  |  |  |  |
Multiemployer pension fund withdrawal liability charge (pre-tax) |  |  | $ 37,922 | $ 37,922 |
Multiemployer pension plans | Asset-Based |  |  |  |  |
Multiemployer Plans |  |  |  |  |
Number of multiemployer plans to which ABF Freight currently contributes | plan |  |  |  | 25 |
Maximum projected time to insolvency for plans in "critical and declining" status |  |  |  | 14 years |
Maximum projected time to insolvency for plans in "critical and declining" status if additional criteria apply |  |  |  | 19 years |
Threshold ratio of inactive to active participants for greater insolvency period to determine "critical and declining" status |  |  |  | 2 |
Threshold funded percentage for greater insolvency period to determine "critical and declining" status |  |  |  | 80.00% |
Multiemployer pension plans | Central States Pension Plan | Asset-Based |  |  |  |  |
Multiemployer Plans |  |  |  |  |
Approximate proportion of multiemployer pension plan contributions (as a percent) |  |  |  | 50.00% |
Multiemployer pension plans | New England Pension Fund | Asset-Based |  |  |  |  |
Multiemployer Plans |  |  |  |  |
Approximate proportion of multiemployer pension plan contributions (as a percent) |  |  |  |  | 3.00%
Multiemployer pension fund withdrawal liability charge (pre-tax) |  | $ 37,900 |  |  |
Discount rate (as a percent) |  | 4.50% | 4.50% | 4.50% |
Initial lump sum cash payment liability |  | $ 15,100 | $ 15,100 | $ 15,100 |
Withdrawal liability monthly payments period (in years) |  | 23 years |  |  |
Aggregate present value of monthly payments |  | $ 22,800 | $ 22,800 | $ 22,800 |
Multiemployer pension plans | New England Pension Fund | Asset-Based | Subsequent Event |  |  |  |  |
Multiemployer Plans |  |  |  |  |
Contribution rate frozen period (in years) | 10 years |  |  |  |

X
- Definition Amount of expenses associated with multiemployer pension fund withdrawal liability. + References No definition available. + Details
Name: | arcb_MultiemployerPensionFundWithdrawalLiabilityCharge
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Represents the percentage of the entity's contributions to multiemployer pension plans that are made to the specified plan. + References No definition available. + Details
Name: | arcb_MultiemployerPensionPlansPercentageOfContributions
Namespace Prefix: | arcb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Discount rate applied to the undiscounted amount of future payments due to determine the present value of the mulitemployer plan withdrawal liability recorded as of the balance sheet date. + References No definition available. + Details
Name: | arcb_MultiemployerPlanWithdrawalLiabilityDiscountRatePercent
Namespace Prefix: | arcb_
Data Type: | num:percentItemType
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X
- Definition The period for which contribution rate is frozen under multiemployer plan agreement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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Namespace Prefix: | arcb_
Data Type: | xbrli:durationItemType
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- Definition The threshold funded percentage of plans, below which a higher maximum period for insolvency is used to determine "critical and declining" status. + References No definition available. + Details
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X
- Definition The threshold ratio of inactive participants to active participants, above which a higher maximum period for insolvency is used to determine "critical and declining" status. + References No definition available. + Details
Name: | arcb_MultiemployerPlansCriticalAndDecliningStatusThresholdRatioOfInactiveToActiveParticipantsForGreaterInsolvencyPeriod
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- Definition The amount of liability of initial lump sum cash payment in order to settle the withdrawal liability from multiemployer plan. + References No definition available. + Details
Name: | arcb_MultiemployerPlansInitialLumpSumCashPayment
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Balance Type: | credit
Period Type: | instant

X
- Definition The maximum period within which a plan in "critical and declining" status is expected to become insolvent, unless additional criteria relating to ratio of inactive to active participants or funded percentage are applicable. + References No definition available. + Details
Name: | arcb_MultiemployerPlansMaximumPeriodOfExpectedInsolvencyForCriticalAndDecliningStatus
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Period Type: | duration

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- Definition The maximum period within which a plan in "critical and declining" status is expected to become insolvent, if additional criteria relating to ratio of inactive to active participants or funded percentage are applicable. + References No definition available. + Details
Name: | arcb_MultiemployerPlansMaximumPeriodOfExpectedInsolvencyForCriticalAndDecliningStatusIfAdditionalCriteriaApply
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- Definition The period of time over which monthly payments have to be made for withdrawal liability settlement for multiemployer plan, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | arcb_MultiemployerPlansMonthlyPaymentsSettlementPeriod
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- Definition Represents the number of multiemployer plans to which the reporting entity currently contributes. + References No definition available. + Details
Name: | arcb_MultiemployerPlansNumber
Namespace Prefix: | arcb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition The aggregate present value of the monthly payments for the multiemployer plan withdrawal liability. + References No definition available. + Details
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Namespace Prefix: | arcb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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- Details
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