Net Loss Per Common Share - Computation of Basic and Diluted Net Loss Per Share (Details) - 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	$ (5,187)	$ (5,416)	$ (11,273)	$ (9,956)
Denominator:
Weighted-average common shares outstanding	12,583,325	3,018,567	12,541,245	3,016,935
Less: weighted-average unvested common shares subjected to repurchase	(169,801)	(461,538)	(184,179)	(461,538)
Weighted-average common shares outstanding used to calculate net loss per common share, basic and diluted	12,413,524	2,557,029	12,357,066	2,555,397
Net loss per common share, basic and diluted	$ (0.42)	$ (2.12)	$ (0.91)	$ (3.90)