CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue	$ 1,692,658	$ 1,142,761	$ 755,932
Costs and expenses:
Cost of revenue	449,358	358,903	241,584
Research and development	606,194	1,207,059	251,662
Sales and marketing	442,807	611,590	259,929
General and administrative	336,803	354,075	77,478
Total costs and expenses	1,835,162	2,531,627	830,653
Loss from operations	(142,504)	(1,388,866)	(74,721)
Interest income	16,119	30,164	13,152
Interest expense and other income (expense), net	(635)	(2,137)	(995)
Loss before provision for income taxes	(127,020)	(1,360,839)	(62,564)
Provision for income taxes	1,303	532	410
Net loss	$ (128,323)	$ (1,361,371)	$ (62,974)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.22)	$ (3.24)	$ (0.50)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	596,264	420,473	127,091