OPERATING SEGMENT DATA - (Rev and Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
REVENUES
Revenues	$ 627,370	$ 771,490	$ 1,328,769	$ 1,483,329
OPERATING EXPENSES
Salaries, wages, and benefits	305,220	361,116	650,166	704,784
Fuel, supplies, and expenses	54,838	80,700	126,611	160,036
Depreciation and amortization	29,086	27,434	58,099	53,971
Gain on sale of property and equipment			(3,581)	(1,469)
Other	29,887	30,987	60,707	63,669
Total consolidated operating expenses	606,945	736,290	1,300,525	1,439,538
OPERATING INCOME (LOSS)
Operating income (loss)	20,425	35,200	28,244	43,791
OTHER INCOME (COSTS)
Interest and dividend income	991	1,616	2,366	3,094
Interest and other related financing costs	(3,378)	(2,811)	(6,325)	(5,693)
Other, net	2,696	(445)	(1,166)	(1,036)
TOTAL OTHER INCOME (COSTS)	309	(1,640)	(5,125)	(3,635)
INCOME BEFORE INCOME TAXES	20,734	33,560	23,119	40,156
Operating Segments | Asset-Based
REVENUES
Revenues	460,070	559,648	975,783	1,065,727
OPERATING EXPENSES
Salaries, wages, and benefits	248,995	297,016	532,833	577,292
Fuel, supplies, and expenses	45,675	65,791	106,900	129,764
Operating taxes and licenses	11,629	12,214	24,423	24,612
Insurance	8,247	7,598	16,071	15,589
Communications and utilities	4,342	4,500	9,053	9,117
Depreciation and amortization	23,327	21,633	46,597	42,594
Rents and purchased transportation	46,152	56,826	101,922	106,132
Shared services	45,605	55,338	94,490	105,633
Gain on sale of property and equipment	(1,175)	(1,587)	(3,339)	(1,621)
Innovative technology costs	4,789	2,735	9,322	4,536
Other	1,448	1,406	3,235	2,286
Total consolidated operating expenses	439,034	523,470	941,507	1,015,934
OPERATING INCOME (LOSS)
Operating income (loss)	21,036	36,178	34,276	49,793
Operating Segments | ArcBest
REVENUES
Revenues	151,467	181,173	316,242	354,377
OPERATING EXPENSES
Purchased transportation	125,090	147,552	262,272	287,657
Supplies and expenses	1,989	2,858	4,269	5,632
Depreciation and amortization	2,449	3,055	4,919	6,206
Shared services	18,840	23,141	40,567	46,172
Other	1,796	2,445	4,321	4,858
Total consolidated operating expenses	150,164	179,051	316,348	350,525
OPERATING INCOME (LOSS)
Operating income (loss)	1,303	2,122	(106)	3,852
Operating Segments | FleetNet
REVENUES
Revenues	46,440	51,722	98,879	104,981
OPERATING EXPENSES
Total consolidated operating expenses	45,658	50,696	97,057	102,467
OPERATING INCOME (LOSS)
Operating income (loss)	782	1,026	1,822	2,514
Other and eliminations
REVENUES
Revenues	(30,607)	(21,053)	(62,135)	(41,756)
OPERATING EXPENSES
Total consolidated operating expenses	(27,911)	(16,927)	(54,387)	(29,388)
OPERATING INCOME (LOSS)
Operating income (loss)	$ (2,696)	$ (4,126)	$ (7,748)	$ (12,368)