OPERATING SEGMENT DATA - Operating expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
OPERATING EXPENSES
Salaries, wages, and benefits	$ 420,643	$ 359,395
Fuel, supplies, and expenses	99,547	73,149
Depreciation and amortization	34,823	30,354
Other	38,254	24,786
Total consolidated operating expenses	1,240,146	797,022
Operating Segments | Asset Based
OPERATING EXPENSES
Salaries, wages, and benefits	313,497	285,694
Fuel, supplies, and expenses	84,831	60,841
Operating taxes and licenses	12,493	12,248
Insurance	10,431	8,939
Communications and utilities	4,687	4,970
Depreciation and amortization	24,305	23,484
Rents and purchased transportation	102,985	75,588
Shared services	67,150	55,866
Gain on sale of property and equipment	(2,695)	(8,695)
Innovative technology costs	6,960	6,868
Other	633	434
Total consolidated operating expenses	625,277	526,237
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	508,380	210,995
Supplies and expenses	3,266	2,568
Depreciation and amortization	5,180	2,386
Shared services	50,197	26,072
Other	7,145	2,050
Total consolidated operating expenses	574,168	244,071
Operating Segments | FleetNet
OPERATING EXPENSES
Total consolidated operating expenses	76,661	58,140
Other and eliminations
OPERATING EXPENSES
Total consolidated operating expenses	$ (35,960)	$ (31,426)