STOCK-BASED COMPENSATION - SUMMARY OF TIME-BASED STOCK OPTIONS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Number of Shares Underlying Stock Options
Ending outstanding balance (in shares)	296
Stock options outstanding
Number of Shares Underlying Stock Options
Beginning outstanding balance (in shares)	828
Exercised (in shares)	(326)
Canceled or expired (in shares)	(206)
Ending outstanding balance (in shares)	296	828
Number of shares underlying stock options, Vested and expected to vest (in shares)	272
Number of shares underlying stock options, Exercisable (in shares)	170
Weighted Average Exercise Price Per Share
Beginning outstanding balance (in dollars per share)	$ 8.16
Exercised (in dollars per share)	8.79
Canceled or expired (in dollars per share)	7.46
Ending outstanding balance (in dollars per share)	7.96	$ 8.16
Weighted average exercise price, Vested and expected to vest (in dollars per share)	7.99
Weighted average exercise price, Exercisable (in dollars per share)	$ 8.20
Weighted average remaining contractual life, Outstanding	3 years 10 months 6 days	4 years 4 months 9 days
Weighted average remaining contractual life, Vested and expected to vest	3 years 8 months 26 days
Weighted average remaining contractual life, Exercisable	2 years 11 months 12 days
Aggregate intrinsic value, Outstanding	$ 171	$ 2,628
Aggregate intrinsic value, Vested and expected to vest	171
Aggregate intrinsic value, Exercisable	$ 171