OPERATING SEGMENT DATA - Operating expenses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING EXPENSES
Salaries, wages, and benefits									$ 1,368,588	$ 1,408,409	$ 1,398,348
Fuel, supplies, and expenses									250,221	316,047	325,126
Depreciation and amortization									118,391	112,466	108,635
Multiemployer pension fund withdrawal liability charge											37,922
Gain on sale of property and equipment									(2,376)	(5,247)	(59)
Other									129,850	126,146	123,998
Asset impairment					$ 26,500					26,514
Restructuring costs											1,655
Gain on sale of subsidiaries											(1,945)
Total consolidated operating expenses	$ 786,162	$ 755,198	$ 606,945	$ 693,580	$ 728,647	$ 756,355	$ 736,290	$ 703,248	2,841,885	2,924,540	2,984,690
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits									1,095,694	1,148,761	1,128,030
Fuel, supplies, and expenses									209,095	257,133	255,655
Operating taxes and licenses									49,300	50,209	48,792
Insurance									33,568	32,516	32,887
Communications and utilities									17,916	18,614	16,983
Depreciation and amortization									94,326	89,798	85,951
Rents and purchased transportation									250,159	221,479	242,247
Shared services									217,258	212,773	215,302
Multiemployer pension fund withdrawal liability charge											37,922
Gain on sale of property and equipment									(3,309)	(5,892)	(410)
Innovative technology costs									22,458	13,739	3,810
Other									6,701	3,488	4,554
Total consolidated operating expenses									1,993,166	2,042,618	2,071,723
Operating Segments | ArcBest
OPERATING EXPENSES
Purchased transportation									649,933	606,113	631,501
Supplies and expenses									9,627	10,789	13,329
Depreciation and amortization									9,714	11,344	13,750
Shared services									90,983	93,961	91,266
Other									9,203	9,860	9,143
Asset impairment										26,514
Restructuring costs											491
Gain on sale of subsidiaries											(1,945)
Total consolidated operating expenses									769,460	758,581	757,535
Operating Segments | FleetNet
OPERATING EXPENSES
Depreciation and amortization									1,622	1,341	1,140
Total consolidated operating expenses									201,682	206,932	190,741
Other and eliminations
OPERATING EXPENSES
Depreciation and amortization									12,729	9,983	7,794
Total consolidated operating expenses									$ (122,423)	$ (83,591)	$ (35,309)