EQUITY-BASED COMPENSATION - Restricted stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
EQUITY-BASED COMPENSATION
Payments for repurchase of common stock	$ 874	$ 6,636
Restricted Stock
EQUITY-BASED COMPENSATION
Compensation expense	$ 1,000	$ 1,900
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	$ 13,600
Weighted-average remaining life	2 years 4 months 24 days
Restricted stock
Beginning balance (in shares)	2,003,072
Granted (in shares)	1,487,448
Vested (in shares)	(484,816)
Forfeited (in shares)	(301,395)
Ending balance (in shares)	2,704,309
Grant Date Fair Value
Beginning balance (in dollars per share)	$ 6.97
Granted (in dollars per share)	6.31
Vested (in dollars per share)	8.71
Forfeited (in dollars per share)	6.38
Ending balance (in dollars per share)	$ 6.36