EQUITY- BASED COMPENSATION - Stock option activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Number of Options
Options, number, Beginning of Period	7,837
Options forfeited, number	(52)
Options expired, number	(362)
Options, number, End of Period	7,423
Options exercisable, number, End of Period	6,559
Options, Weighted Average Exercise Price
Options, Beginning of Period, weighted average exercise price	$ 1.49
Options forfeited, weighted average exercise price	2.28
Options expired, weighted average exercise price	1.43
Options, End of Period, weighted average exercise price	1.49
Options exercisable, End of Period, weighted average exercise price	$ 1.48
Weighted Average Remaining Contractual Term
Options, End of Period, weighted average remaining contractual term	5 years 1 month 6 days
Options exercisable, End of Period, weighted average remaining contractual term	5 years
Aggregate Intrinsic Value
Options, End of Period, aggregate intrinsic value	$ 47
Options exercisable, End of Period, aggregated intrinsic value	26
Unrecognized compensation, non-vested options	$ 204
Unrecognized compensation, options with milestone-based vesting		$ 637
Employee Stock Option
Aggregate Intrinsic Value
Unrecognized compensation, period for recognition	8 months 12 days