Net Loss Per Share Attributable to Common Shareholders - Computation of the Basic and Diluted Net Loss Per Share Attributable to Common Shareholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (68,606)	$ (46,447)	$ (42,831)
Fair value adjustments to redemption value for Series E-1 convertible preferred stock options	(964)	102	135
Net loss attributable to common shareholders	$ (69,570)	$ (46,345)	$ (42,696)
Weighted-average shares used in computing net loss per share	69,165,315	12,629,778	12,196,998
Net loss per share attributable to common shareholders, basic and diluted	$ (1.01)	$ (3.67)	$ (3.50)