Net Loss per Share - Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (5,023)	$ (4,390)	$ (6,748)	$ (7,749)	$ (7,172)	$ (7,213)	$ (16,161)	$ (22,134)
Denominator:
Weighted average common shares outstanding—basic and diluted.	39,321,177			27,810,358			32,808,082	23,431,823
Total	39,321,177			27,810,358			32,808,082	23,431,823
Net loss per share —basic and diluted	$ (0.13)			$ (0.28)			$ (0.49)	$ (0.95)