Net Loss per Share - Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss used to compute net loss per share, basic and diluted	$ (471,716)	$ (229,743)	$ (124,827)
Denominator:
Weighted-average number of shares used in computing net loss per share, basic	90,558	81,011	69,555
Weighted-average number of shares used in computing net loss per share, diluted	90,558	81,011	69,555
Net loss per share, basic (in dollars per share)	$ (5.21)	$ (2.84)	$ (1.79)
Net loss per share, diluted (in dollars per share)	$ (5.21)	$ (2.84)	$ (1.79)
Potentially dilutive shares not included in diluted per share calculation	17,683	18,343	10,933
Convertible Notes
Denominator:
Convertible, If-converted value in excess of principal	$ 441,900
Potentially dilutive shares not included in diluted per share calculation	7,411	7,411