Organization and Summary of Significant Accounting Policies - Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (32,034)	$ (35,308)	$ (52,405)	$ (79,679)	$ (58,434)	$ (73,643)	$ (62,887)	$ (83,053)	$ (199,426)	$ (278,017)	$ (236,455)
Denominator:
Weighted-average ordinary shares outstanding									69,518	62,808	56,452
Less: weighted-average ordinary shares subject to forfeiture									(57)	(463)	(842)
Weighted-average shares used to compute basic net loss per share									69,461	62,345	55,610
Weighted-average shares used to compute diluted net loss per share									69,461	62,345	55,610
Basic net loss per share	$ (0.43)	$ (0.48)	$ (0.80)	$ (1.24)	$ (0.92)	$ (1.16)	$ (1.00)	$ (1.40)	$ (2.87)	$ (4.46)	$ (4.25)
Diluted net loss per share	$ (0.43)	$ (0.48)	$ (0.80)	$ (1.24)	$ (0.92)	$ (1.16)	$ (1.00)	$ (1.40)	$ (2.87)	$ (4.46)	$ (4.25)