POSTRETIREMENT BENEFIT PLANS - Multiemployer Plans (Details) - Nonunion Defined Benefit Pension Plan - Asset Based - plan	3 Months Ended
Mar. 31, 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%

Represents the projected funded percentage of a specified multiemployer pension plan.

No definition available.

Name:	arcb_MultiemployerPensionPlanFundedPercentage
Namespace Prefix:	arcb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

- 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

- 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

- 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

- 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

- 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

- 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

- Details

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

- Details

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

- Details

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