OPERATING SEGMENT DATA - Revenue (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
Revenues
Revenues	$ 816,414	$ 794,980	$ 627,370	$ 701,399	$ 717,418	$ 787,563	$ 771,490	$ 711,839	$ 2,940,163	$ 2,988,310	$ 3,093,788
Asset Based
Revenues
Revenues									1,998,549	2,077,287	2,131,571
ArcBest
Revenues
Revenues									770,560	731,366	773,968
FleetNet
Revenues
Revenues									166,654	175,055	182,861
Other
Revenues
Revenues									4,400	4,602	5,388
Operating Segments | Asset Based
Revenues
Revenues									2,092,031	2,144,679	2,175,585
Operating Segments | ArcBest
Revenues
Revenues									779,115	738,392	781,123
Operating Segments | FleetNet
Revenues
Revenues									205,049	211,738	195,126
Other and eliminations
Revenues
Revenues									(136,032)	(106,499)	(58,046)
Intersegment revenues
Revenues
Revenues									(140,432)	(111,101)	(63,434)
Intersegment revenues | Asset Based
Revenues
Revenues									93,482	67,392	44,014
Intersegment revenues | ArcBest
Revenues
Revenues									8,555	7,026	7,155
Intersegment revenues | FleetNet
Revenues
Revenues									$ 38,395	$ 36,683	$ 12,265