COMMON STOCK AND STOCKHOLDERS' EQUITY - SUMMARY OF STOCK OPTION ACTIVITY (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding at the beginning of period (in shares)	4,311,463
Granted (in shares)	612,144
Exercised (in shares)	(679,175)
Forfeited or canceled (in shares)	(187,185)
Options outstanding at the end of period (in shares)	4,057,247	4,311,463
Exercisable (in shares)	2,089,327
Vested and expected to vest (in shares)	3,988,909
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options oustanding, beginning balance (in dollars per share)	$ 9.87
Granted (in dollars per share)	13.89
Exercised (in dollars per share)	7.45
Forfeited or canceled (in dollars per share)	12.68
Options outstanding, ending balance (in dollars per share)	10.75	$ 9.87
Exercisable (in dollars per share)	7.93
Vested and expected to vest (in dollars per share)	$ 10.70
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Life (years), Outstanding	7 years 10 months 24 days	7 years 10 months 24 days
Weighted Average Remaining Contractual Life (years), Granted	9 years 4 months 24 days
Weighted Average Remaining Contractual Life (years), Options exercisable	6 years 7 months 24 days
Weighted Average Remaining Contractual Life (years), Options vested and expected to vest	7 years 7 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 36,161	$ 22,709
Aggregate Intrinsic Value, Options Exercisable	24,514
Aggregate Intrinsic Value, Options vested and expected to vest	$ 35,755