DEFINED CONTRIBUTION PLAN (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
DEFINED CONTRIBUTION PLAN
Company's expense under matching requirements	$ 1.1	$ 0.6	$ 1.9	$ 1.2
Matching contribution not yet merged	$ 0.1	$ 0.0	$ 0.2	$ 0.0