GOODWILL AND INTANGIBLE ASSETS - Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
Goodwill by reportable operating segment
Balance at the beginning of the period	$ 300,337
Purchase accounting adjustment	(1,329)
Balance at the end of the period	299,008
ArcBest
Goodwill by reportable operating segment
Balance at the beginning of the period	299,707
Purchase accounting adjustment	(1,329)
Balance at the end of the period	298,378
FleetNet
Goodwill by reportable operating segment
Balance at the beginning of the period	630
Balance at the end of the period	$ 630