OPERATING SEGMENT DATA - Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
OPERATING INCOME
Operating income	$ 32,191	$ 7,819
OTHER INCOME (COSTS)
Interest and dividend income	392	1,375
Interest and other related financing costs	(2,428)	(2,947)
Other, net	1,192	(3,862)
TOTAL OTHER INCOME (COSTS)	(844)	(5,434)
INCOME BEFORE INCOME TAXES	31,347	2,385
Operating Segments | Asset Based
OPERATING INCOME
Operating income	30,055	13,240
Operating Segments | ArcBest
OPERATING INCOME
Operating income	8,265	(1,409)
Operating Segments | FleetNet
OPERATING INCOME
Operating income	1,023	1,040
Other and eliminations
OPERATING INCOME
Operating income	$ (7,152)	$ (5,052)