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POSTRETIREMENT BENEFIT PLANS - Additional information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Postretirement benefit plans
Pension settlement expense	$ 89
Pension settlement expense, net of tax	66
Supplemental Benefit Plan
Postretirement benefit plans
Pension settlement expense	89
Pension settlement expense, net of tax	100
Benefit related to an officer retirement	$ 700

X

- Definition

The amount of benefit due upon retirement, including the portion for which distribution is delayed in accordance with IRC Section 409A.

+ References

No definition available.

+ Details

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

X

- Definition

Net of tax amount of the gain (loss) adjustment to other comprehensive income (loss) resulting from the settlement of the entity's defined benefit pension and other postretirement plans.

+ References

No definition available.

+ Details

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Namespace Prefix:	arcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919

Reference 3: 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=118255775&loc=d3e2709-114920

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: