v3.8.0.1
NET LOSS PER SHARE - Antidilutive Securities (Details) - shares
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Shares excluded from the diluted per share calculation 9,685,425 11,949,359
Shares of common stock issuable under the Equity Incentive Plan    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Shares excluded from the diluted per share calculation 9,254,272 11,557,330
Employee Stock Purchase Plan    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Shares excluded from the diluted per share calculation 431,153 392,029