GOODWILL AND INTANGIBLE ASSETS (Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 01, 2015	Jan. 02, 2015
Goodwill by reportable operating segment
Balance at the beginning of the period	$ 96,465	$ 77,078
Goodwill acquired	12,640	19,387
Goodwill divested	(842)
Purchase accounting adjustments	612
Balance at the end of the period	108,875	96,465
FleetNet
Goodwill by reportable operating segment
Balance at the beginning of the period	630	630
Balance at the end of the period	630	630
ArcBest
Goodwill by reportable operating segment
Balance at the beginning of the period	95,835	76,448
Goodwill acquired	12,640	19,387
Goodwill divested	(842)
Purchase accounting adjustments	612
Balance at the end of the period	$ 108,245	$ 95,835
Smart Lines Transportation Group, LLC
Goodwill by reportable operating segment
Goodwill related to acquisition expected to be fully tax deductible				$ 4,200
Bear Transportation Services, L.P.
Goodwill by reportable operating segment
Goodwill related to acquisition expected to be fully tax deductible			$ 15,200