-- None. No documentation exists for this element. --

No definition available.

Name:	arcb_DefinedBenefitPlanDistributionsAndPensionSettlementExpenseAbstract
Namespace Prefix:	arcb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of lump sum benefit distributions paid.

+ References

No definition available.

+ Details

Name:	arcb_DefinedBenefitPlanLumpSumDistributionPaid
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the period of delay provision for key employees as required by Section 409A of the Internal Revenue Code related to lump-sum termination payment.

+ References

No definition available.

+ Details

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

- Definition

The amount of net gain (loss), per diluted share, net of taxes, 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.

+ References

No definition available.

+ Details

Name:	arcb_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsPerDilutedShareNetOfTaxes
Namespace Prefix:	arcb_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount paid for nonparticipating annuity contract to settle vested benefit obligations of participants and beneficiaries receiving monthly benefits.

+ References

No definition available.

+ Details

Name:	arcb_NonparticipatingAnnuityContractPremiumPaid
Namespace Prefix:	arcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanSettlementsPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix:
Data Type:	na
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EMPLOYEE BENEFIT PLANS (Settlement distributions and expense) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Distributions and pension settlement expense
Pension settlement expense, pre-tax		$ 12,925	$ 4,156	$ 3,229
Nonunion Defined Benefit Pension Plan
Distributions and pension settlement expense
Pension settlement distributions		105,279	26,261	16,515
Pension settlement expense, pre-tax		$ 12,925	$ 4,156	$ 3,023
Pension settlement expense per diluted share, net of taxes		$ 0.36	$ 0.10	$ 0.07
Lump-sum distributions			$ 18,700
Nonparticipating annuity contract	$ 7,600		7,600
Supplemental Benefit Plan
Distributions and pension settlement expense
Pension settlement distributions			$ 989	$ 246
Pension settlement expense, pre-tax				$ 206
Pension settlement expense per diluted share, net of taxes				$ 0.01
Period of delay for pension settlement distribution to key employees				6 months