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POSTRETIREMENT BENEFIT PLANS - Additional information (Details) $ in Thousands | 9 Months Ended
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Sep. 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

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- 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

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- 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

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- 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

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- 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=123447040&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=123453770&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=123447040&loc=d3e2709-114920 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |