Net Loss per Share - Summary of Basic and Diluted Net loss per Share Attributable to Common Stockholders (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	$ (17,449)	$ (15,144)	$ (11,138)	$ (17,714)	$ (13,383)	$ (10,873)	$ (43,731)	$ (41,970)
Accruing dividends on Series A convertible preferred stock	0			0			0	(592)
Net loss attributable to common stockholders	$ (17,449)			$ (17,714)			$ (43,731)	$ (42,562)
Denominator:
Weighted average common shares outstanding—basic and diluted (in shares)	20,085,000			14,562,000			20,035,000	9,866,000
Net loss per share attributable to common stock holders—basic and diluted (usd per share)	$ (0.87)			$ (1.22)			$ (2.18)	$ (4.31)