Net Loss Per Share - Computation of Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss – Basic and diluted		$ (122,461)	$ (23,605)	$ (27,780)
Net loss – Basic and diluted		$ (122,461)	$ (23,605)	$ (27,780)
Denominator:
Weighted average common shares outstanding - basic and diluted (in shares)	[1]	294,549,146	261,228,108	236,040,717
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	[1]	$ (0.42)	$ (0.09)	$ (0.12)

[1] Retroactively restated for the reverse recapitalization as described in Notes 1 and 2.