Net Loss Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Numerator:                      
Net loss                 $ (57,878) $ (74,286) $ (36,478)
Accretion of redeemable convertible preferred stock to redemption value                     (92)
Net loss attributable to common stockholders $ (10,439) $ (14,675) $ (15,028) $ (17,736) $ (23,174) $ (19,884) $ (17,756) $ (13,472) $ (57,878) $ (74,286) $ (36,570)
Denominator:                      
Weighted average common shares outstanding, basic and diluted 27,332,515 27,322,907 27,272,225 27,263,435 27,238,079 27,138,667 27,011,960 25,615,282 27,297,934 26,756,079 12,189,155
Net loss per share attributable to common stockholders, basic and diluted $ (0.38) $ (0.54) $ (0.55) $ (0.65) $ (0.85) $ (0.73) $ (0.66) $ (0.53) $ (2.12) $ (2.78) $ (3.00)