Net Loss Per Share - Schedule of Antidilutive Securities, Excluded from Computation of Diluted Net Loss per Share (Detail) - shares
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock 2,134,458 1,730,136 13,416,167
Options to Purchase Common Stock [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock 2,115,519 1,611,991 924,132
Non-vested Restricted Stock [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock   28,437  
Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock     12,440,205
Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member] | Warrant [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock     51,830
Common Stock [Member] | Warrant [Member]      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock 18,939 89,708