NET LOSS PER SHARE - SUMMARY OF ANTI-DILUTIVE LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS (Details) - shares	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	4,811,931	4,519,766
Outstanding Stock Options and Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	4,093,778	4,519,766
Outstanding Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	718,153	0