GOODWILL AND INTANGIBLE ASSETS (Goodwill) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill by reportable operating segment
Balance at the beginning of the period	$ 108,875
Purchase accounting adjustments	106
Balance at the end of the period	108,981
ArcBest
Goodwill by reportable operating segment
Balance at the beginning of the period	108,245
Purchase accounting adjustments	106
Balance at the end of the period	108,351
FleetNet
Goodwill by reportable operating segment
Balance at the beginning of the period	630
Balance at the end of the period	$ 630