EQUITY-BASED COMPENSATION - Restricted stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restricted Stock
EQUITY-BASED COMPENSATION
Compensation expense	$ 1.9	$ 2.2	$ 3.8	$ 4.0
Restricted Stock | Minimum
EQUITY-BASED COMPENSATION
offering period			1 year
Restricted Stock | Maximum
EQUITY-BASED COMPENSATION
offering period			3 years
Restricted Stock Awards
EQUITY-BASED COMPENSATION
Unrecognized compensation expense	$ 11.4		$ 11.4
Weighted-average remaining life			1 year 7 months 6 days
Restricted stock
Beginning balance (in shares)			1,518,193
Granted (in shares)			1,477,488
Vested (in shares)			(561,682)
Forfeited (in shares)			(340,328)
Ending balance (in shares)	2,093,671		2,093,671
Grant Date Fair Value
Beginning balance (in dollars per share)			$ 10.08
Granted (in dollars per share)			5.80
Vested (in dollars per share)			11.92
Forfeited			7.55
Ending balance (in dollars per share)	$ 6.98		$ 6.98
Restricted Stock Units
Restricted stock
Beginning balance (in shares)			1,250
Vested (in shares)			(625)
Forfeited (in shares)			(625)
Grant Date Fair Value
Beginning balance (in dollars per share)			$ 19.00
Vested (in dollars per share)			20.00
Forfeited			$ 18.00