ORGANIZATION AND DESCRIPTION OF THE BUSINESS AND FINANCIAL STATEMENT PRESENTATION (ASC Topic 606) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
ASC Topic 606
Retained earnings	$ 449,442		$ 449,442			$ 438,379
Revenues	793,350	$ 720,368	1,493,351	$ 1,371,456
Difference between Revenue Guidance in Effect before and after Topic 606 | ASC Topic 606, Revenue from Contracts with Customers
ASC Topic 606
Retained earnings					$ 400
Revenues	1,100		800
Purchased transportation	$ 800		$ 500