Net Loss Per Common Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net loss	$ (6,086)	$ (4,540)
Denominator:
Weighted-average common shares outstanding	12,498,698	3,015,303
Less: weighted-average unvested common shares subjected to repurchase	(198,717)	(461,538)
Weighted-average common shares outstanding used to calculate net loss per common share, basic and diluted	12,299,981	2,553,765
Net loss per common share, basic and diluted	$ (0.49)	$ (1.78)