Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (34,495)	$ (41,975)	$ (34,346)
Denominator:
Weighted-average shares outstanding	24,783,287	12,669,367	1,338,776
Less: weighted-average shares of restricted stock that are subject to repurchase	(61,512)	(172,410)	(382,524)
Weighted-average shares used in computing net loss per share attributable to common stock, basic and diluted	24,721,775	12,496,957	956,252
Net loss per share attributable to common stockholders, basic and diluted	$ (1.40)	$ (3.36)	$ (35.92)