STOCK-BASED COMPENSATION - Option activity (Details) - 2016 Omnibus Incentive Plan	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Number of options
Options outstanding, beginning of period (in shares) | shares	4,803,146
Granted (in shares) | shares	96,765
Exercised (in shares) | shares	(44,225)
Forfeited (in shares) | shares	(62,710)
Options outstanding, end of period (in shares) | shares	4,792,976
Vested and expected to vest, end of period (in shares) | shares	4,792,976
Exercisable, end of period (in shares) | shares	3,272,342
Weighted-average exercise price
Options outstanding, weighted-average exercise price, beginning period (in USD per share) | $ / shares	$ 12.29
Granted, weighted average exercise price (in USD per share) | $ / shares	7.58
Exercised, weighted average exercise price (in USD per share) | $ / shares	3.50
Forfeited, weighted average exercise price (in USD per share) | $ / shares	16.27
Options outstanding, weighted-average exercise price, end of period (in USD per share) | $ / shares	12.22
Vested and expected to vest, weighted-average exercise price, end of period (in USD per share) | $ / shares	12.22
Exercisable, weighted-average exercise price (in USD per share) | $ / shares	$ 9.70