COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Letter of credit
Operating Leased Assets [Line Items]
Outstanding letters of credit	$ 10.6		$ 10.6
Revenue Equipment
Operating Leased Assets [Line Items]
Rent expense	4.6	$ 4.1	9.0	$ 7.9
Office and Terminals
Operating Leased Assets [Line Items]
Rent expense	$ 3.0	$ 1.6	$ 5.7	$ 2.4