Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net loss	$ (10,694)	$ (10,632)	$ (36,604)	$ (15,849)
Accretion of convertible preferred stock to redemption value		(1,020)		(2,353)
Net loss attributable to common stockholders	$ (10,694)	$ (11,652)	$ (36,604)	$ (18,202)
Denominator:
Weighted average shares of common stock outstanding (in shares)	21,415,871	2,730,427	20,752,590	2,730,427
Less: Weighted average shares of unvested restricted common stock outstanding (in shares)		(455,810)		(574,742)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders, basic and diluted (in shares)	21,415,871	2,274,617	20,752,590	2,155,685
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.50)	$ (5.12)	$ (1.76)	$ (8.44)