OPERATING SEGMENT DATA - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues
Revenues	$ 829,213	$ 701,399
Asset Based
Revenues
Revenues	529,724	495,728
ArcBest
Revenues
Revenues	250,241	162,948
FleetNet
Revenues
Revenues	48,434	41,744
Operating Segments | Asset Based
Revenues
Revenues	556,292	515,713
Operating Segments | ArcBest
Revenues
Revenues	252,336	164,775
Operating Segments | FleetNet
Revenues
Revenues	59,163	52,439
Other and eliminations
Revenues
Revenues	$ (38,578)	$ (31,528)