Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenue		$ 455.0	$ 385.6
Cost of revenue	[1]	103.1	98.4
Gross profit		351.9	287.2
Operating expenses
Research and development	[1]	181.8	150.0
Sales and marketing	[1]	104.3	101.5
General and administrative(2)	[1],[2]	39.0	57.0
Total operating expenses	[1]	325.1	308.5
Income (loss) from operations		26.8	(21.3)
Interest income, net		2.4	3.7
Other income, net		10.6	4.2
Income (loss) before income taxes		39.8	(13.4)
Benefit from (provision for) income taxes		(0.5)	5.7
Net income (loss)		$ 39.3	$ (7.7)
Net income (loss) per share attributable to common stockholders, basic (in dollars per share)		$ 0.09	$ (0.02)
Net income (loss) per share attributable to common stockholders, diluted (in dollars per share)		$ 0.09	$ (0.02)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic (in shares)		417.3	410.5
Weighted-average shares used in computing net loss per share attributable to common stockholders,diluted (in shares)		419.3	410.5

[1] Includes stock-based compensation as follows (in millions):
  Three months ended
March 31,     2020   2019             Cost of revenue $ 3.5
  $ 3.0
  Research and development 37.2
  30.5
  Sales and marketing 6.7
  7.1
  General and administrative⁽²⁾ (7.6 )   15.0
 

[2] On March 19, 2020, one of the Company's co-founders resigned as a member of the board and as an officer of the Company, resulting in the reversal of $23.8 million in stock-based compensation expense. Of the total amount reversed, $21.5 million related to expense recognized prior to December 31, 2019. See Note 12 "Stockholders' Equity" for further information.