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	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (4,926)	$ (10,969)	$ (29,360)	$ (31,194)
Denominator:
Weighted-average shares outstanding	28,447,329	20,307,383	23,305,249	10,087,459
Less: weighted-average unvested restricted shares and shares subject to repurchase	(50,659)	(149,160)	(70,031)	(191,885)
Weighted-average shares used in computing net loss per share attributable to common stock, basic and diluted	28,396,670	20,158,223	23,235,218	9,895,574
Net loss per share attributable to common stockholders, basic and diluted	$ (0.17)	$ (0.54)	$ (1.26)	$ (3.15)