LONG-TERM DEBT AND FINANCING ARRANGEMENTS (Financing arrangements - Credit Facility) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Aug. 31, 2019
Credit Facility
Financing Arrangements
Maximum borrowing capacity	$ 250.0	$ 200.0
Additional borrowing capacity that may be requested	125.0	$ 100.0
Remaining borrowing capacity	180.0
Swing Line Facility
Financing Arrangements
Maximum borrowing capacity	25.0
Letters of Credit, Sub-Facility
Financing Arrangements
Maximum borrowing capacity	$ 20.0

Additional borrowing capacity that may be requested by the entity under the credit facility, subject to conditions contained in the debt agreement.

No definition available.

+ Details

Name:	arcb_LineOfCreditFacilityAdditionalBorrowingCapacity
Namespace Prefix:	arcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=arcb_RevolvingCreditFacilitySwingLineFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=arcb_LettersOfCreditSubCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: