COMMON STOCK AND STOCKHOLDERS' EQUITY - SUMMARY OF STOCK OPTION ACTIVITY (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding at the beginning of period (in shares)	3,843,276
Granted (in shares)	549,759
Exercised (in shares)	(411,076)
Forfeited or canceled (in shares)	(112,249)
Options outstanding at the end of period (in shares)	3,869,710	3,843,276
Exercisable (in shares)	2,091,253
Vested and expected to vest (in shares)	3,818,858
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options oustanding, beginning balance (in dollars per share)	$ 10.93
Granted (in dollars per share)	25.68
Exercised (in dollars per share)	11.03
Forfeited or canceled (in dollars per share)	15.25
Options outstanding, ending balance (in dollars per share)	12.89	$ 10.93
Exercisable (in dollars per share)	8.78
Vested and expected to vest (in dollars per share)	12.80
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 11.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Life (years), Outstanding	7 years 3 months 18 days	7 years 6 months
Weighted Average Remaining Contractual Life (years), Options exercisable	6 years 2 months 12 days
Weighted Average Remaining Contractual Life (years), Options vested and expected to vest	7 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding	$ 55,445	$ 39,902
Aggregate Intrinsic Value, Exercised	6,648
Aggregate Intrinsic Value, Options Exercisable	38,511
Aggregate Intrinsic Value, Options vested and expected to vest	$ 55,038