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POSTRETIREMENT BENEFIT PLANS - Multiemployer Plans (Details) - Nonunion Defined Benefit Pension Plan - Asset Based - plan | 6 Months Ended |
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Jun. 30, 2021 | Jan. 01, 2020
Multiemployer Plans |  |
Number of multiemployer plans to which ABF Freight currently contributes | 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% |
Central States Pension Plan |  |
Multiemployer Plans |  |
Approximate proportion of multiemployer pension plan contributions (as a percent) | 50.00% |
Actuarially certified projected funded percentage of multiemployer pension plan |  | 19.50%

X
- Definition Represents the projected funded percentage of a specified multiemployer pension plan. + References No definition available. + Details
Name: | arcb_MultiemployerPensionPlanFundedPercentage
Namespace Prefix: | arcb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- 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 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
Name: | arcb_MultiemployerPlansCriticalAndDecliningStatusThresholdFundedPercentageForGreaterInsolvencyPeriod
Namespace Prefix: | arcb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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
Namespace Prefix: | arcb_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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
Namespace Prefix: | arcb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- 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
Namespace Prefix: | arcb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_MultiemployerPlansLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=arcb_AssetBasedSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=arcb_CentralStatesPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |