OPERATING SEGMENT DATA - Operating expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
OPERATING EXPENSES
Salaries, wages, and benefits	$ 449,404	$ 389,146	$ 870,047	$ 748,541
Fuel, supplies, and expenses	119,378	80,020	218,925	153,169
Depreciation and amortization	35,330	30,282	70,153	60,636
Gain on sale of subsidiary			(402)	(6,923)
Gain on sale of property and equipment			(4,073)	(8,408)
Other	40,594	27,466	78,848	52,252
Total consolidated operating expenses	1,255,583	874,674	2,495,729	1,671,696
Asset Based
OPERATING EXPENSES
Gain on sale of property and equipment			(4,100)	(8,600)
ArcBest
OPERATING EXPENSES
Gain on sale of subsidiary		(6,900)		(6,900)
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits	328,068	302,370	641,565	588,064
Fuel, supplies, and expenses	99,296	64,689	184,127	125,530
Operating taxes and licenses	12,823	12,303	25,316	24,551
Insurance	12,197	9,454	22,628	18,393
Communications and utilities	4,648	4,663	9,335	9,633
Depreciation and amortization	24,463	23,308	48,768	46,792
Rents and purchased transportation	121,550	95,082	224,535	170,670
Shared services	75,584	69,372	142,734	125,238
Gain on sale of property and equipment	(1,370)	71	(4,065)	(8,624)
Innovative technology costs	7,954	7,532	14,914	14,400
Other	753	77	1,386	511
Total consolidated operating expenses	685,966	588,921	1,311,243	1,115,158
Operating Segments | Asset Based | Land and structures
OPERATING EXPENSES
Gain on sale of property and equipment				(8,600)
Operating Segments | ArcBest
OPERATING EXPENSES
Purchased transportation	448,160	226,603	956,540	437,598
Supplies and expenses	4,263	2,476	7,529	5,044
Depreciation and amortization	5,468	2,366	10,648	4,752
Shared services	57,986	29,078	108,183	55,150
Gain on sale of subsidiary	(402)	(6,923)	(402)	(6,923)
Other	6,701	2,021	13,846	4,071
Total consolidated operating expenses	522,176	255,621	1,096,344	499,692
Operating Segments | FleetNet
OPERATING EXPENSES
Total consolidated operating expenses	80,540	58,409	157,201	116,549
Other and eliminations
OPERATING EXPENSES
Total consolidated operating expenses	$ (33,099)	$ (28,277)	$ (69,059)	$ (59,703)