Net Loss per Share - Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net loss	$ (4,390)	$ (6,748)	$ (7,172)	$ (7,213)	$ (11,138)	$ (14,385)
Denominator:
Weighted average common shares outstanding—basic and diluted.	31,221,139		26,453,428		29,515,749	20,666,988
Weighted average pre-funded warrants to purchase common stock.			1,072,637			539,281
Total	31,221,139		27,526,065		29,515,749	21,206,269
Net loss per share —basic and diluted	$ (0.14)		$ (0.26)		$ (0.38)	$ (0.68)