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INCOME TAXES (Tax Rate) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
INCOME TAXES
Effective tax rate (as a percent)	24.90%	30.30%	24.30%	28.30%
State tax, low end of range of rate (as a percent)			6.00%
State tax, high end of range of rate (as a percent)			6.50%

X

- Definition

Represents the high end of the range of average state tax rates during the period.

+ References

No definition available.

+ Details

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X

- Definition

Represents the low end of the range of average state tax rates during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	arcb_
Data Type:	num:percentItemType
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X

- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

+ Details

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- References

No definition available.

+ Details

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