CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 442,616	$ 279,703	$ 987,041	$ 742,863
Costs and expenses:
Cost of revenue	112,844	83,520	320,335	262,629
Research and development	160,187	167,703	442,484	1,042,026
Sales and marketing	118,531	110,740	322,041	484,053
General and administrative	148,087	51,450	249,834	299,834
Total costs and expenses	539,649	413,413	1,334,694	2,088,542
Loss from operations	(97,033)	(133,710)	(347,653)	(1,345,679)
Interest income	2,896	9,837	14,265	22,023
Interest expense and other income (expense), net	(51)	(1,056)	(2,144)	(2,004)
Loss before provision for income taxes	(94,188)	(124,929)	(335,532)	(1,325,660)
Provision for (benefit from) income taxes	32	(197)	632	(7)
Net loss	$ (94,220)	$ (124,732)	$ (336,164)	$ (1,325,653)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.16)	$ (0.23)	$ (0.57)	$ (4.15)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	603,490	546,126	588,895	319,490