Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Earnings Per Share [Abstract]
Net loss	$ (30,737)	$ 13,224	$ (41,248)	$ (6,683)	$ (322)	$ (5,242)	$ (58,761)	$ (12,247)
Accretion of redeemable series A-1 preferred stock	(6,542)			(5,030)			(17,601)	(14,341)
Redeemable series A-1 preferred stock deemed dividend	(24,341)						(24,341)
Convertible and redeemable series A-2 preferred stock dividend	(2,870)						(2,870)
Net loss attributable to common stockholders – basic and diluted	$ (64,490)			$ (11,713)			$ (103,573)	$ (26,588)
Weighted-average common shares outstanding – basic and diluted	21,554			8,718			13,669	8,640
Net loss per share attributable to common stockholders – basic and diluted	$ (2.99)			$ (1.34)			$ (7.58)	$ (3.08)