Net Loss per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (14,979)	$ (7,098)	$ (29,080)	$ (18,845)
Accretion of redeemable convertible preferred stock	0	(225)	0	(265)
Net loss attributable to common stockholders	$ (14,979)	$ (7,323)	$ (29,080)	$ (19,110)
Denominator:
Weighted-average shares used to compute net loss per common share, basic and diluted	16,875,627	383,910	16,821,225	335,855
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.89)	$ (19.07)	$ (1.73)	$ (56.90)