Net Loss Per Share - Computation of Basic and Diluted Net Loss Per Share (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	$ (459,517)	$ (437,112)	$ (398,073)	$ (463,477)	$ (644,239)	$ (1,138,473)	$ (1,294,702)	$ (2,246,189)
Weighted-average shares used in computing net loss per share, basic and diluted (in shares)	314,530			294,784			309,433	203,199
Net loss per share, basic and diluted (in dollars per share)	$ (1.46)			$ (1.57)			$ (4.18)	$ (11.05)