Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Class A and Class B common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjustment Accumulated deficit
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Shares outstanding, beginning of the period (in shares) at Dec. 31, 2018		409.6
Shareholders equity, beginning balance at Dec. 31, 2018	$ 676.8	$ 0.0	$ 2,337.5	$ (1,659.5)	$ (1.2)	$ 1.0	$ 1.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Release of restricted stock units and awards (in shares)		8.5
Shares repurchased for tax withholdings on release of restricted stock units and awards (in shares)		(3.1)
Shares repurchased for tax withholdings on release of restricted stock	(67.1)		(53.6)	(13.5)
Exercise of stock options and awards (in shares)		0.3
Exercise of stock options and awards	2.0		2.0
Assumed stock options in connection with acquisition	0.8		0.8
Stock-based compensation	191.9		191.9
Other comprehensive income	3.3				3.3
Net income (loss)	(46.1)			(46.1)
Shares outstanding, end of the period (in shares) at Sep. 30, 2019		415.3
Shareholders equity, ending balance at Sep. 30, 2019	762.6	$ 0.0	2,478.6	(1,718.1)	2.1
Shares outstanding, beginning of the period (in shares) at Jun. 30, 2019		413.4
Shareholders equity, beginning balance at Jun. 30, 2019	730.2	$ 0.0	2,428.4	(1,700.1)	1.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Release of restricted stock units and awards (in shares)		3.0
Shares repurchased for tax withholdings on release of restricted stock units and awards (in shares)		(1.1)
Shares repurchased for tax withholdings on release of restricted stock	(19.0)		(18.0)	(1.0)
Exercise of stock options and awards (in shares)		0.0
Exercise of stock options and awards	0.0		0.0
Stock-based compensation	68.2		68.2
Other comprehensive income	0.2				0.2
Net income (loss)	(17.0)			(17.0)
Shares outstanding, end of the period (in shares) at Sep. 30, 2019		415.3
Shareholders equity, ending balance at Sep. 30, 2019	762.6	$ 0.0	2,478.6	(1,718.1)	2.1
Shares outstanding, beginning of the period (in shares) at Dec. 31, 2019		417.0
Shareholders equity, beginning balance at Dec. 31, 2019	$ 808.4	$ 0.0	2,531.3	(1,726.2)	3.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Release of restricted stock units and awards (in shares)		9.4
Shares repurchased for tax withholdings on release of restricted stock units and awards (in shares)	(3.3)	(3.3)
Shares repurchased for tax withholdings on release of restricted stock	$ (66.5)		(31.0)	(35.5)
Repurchases of common stock (in shares)		(9.2)
Repurchases of common stock	$ (177.3)		(85.2)	(92.1)
Exercise of stock options and awards (in shares)	0.4	0.4
Exercise of stock options and awards	$ 1.6		1.6
Stock-based compensation	192.1		192.1
Other comprehensive income	3.5				3.5
Net income (loss)	89.5			89.5
Shares outstanding, end of the period (in shares) at Sep. 30, 2020		414.3
Shareholders equity, ending balance at Sep. 30, 2020	851.3	$ 0.0	2,608.8	(1,764.3)	6.8
Shares outstanding, beginning of the period (in shares) at Jun. 30, 2020		413.8
Shareholders equity, beginning balance at Jun. 30, 2020	803.4	$ 0.0	2,560.4	(1,764.4)	7.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Release of restricted stock units and awards (in shares)		3.3
Shares repurchased for tax withholdings on release of restricted stock units and awards (in shares)		(1.1)
Shares repurchased for tax withholdings on release of restricted stock	(22.5)		(10.6)	(11.9)
Repurchases of common stock (in shares)		(1.8)
Repurchases of common stock	(37.5)		(16.8)	(20.7)
Exercise of stock options and awards (in shares)		0.1
Exercise of stock options and awards	0.1		0.1
Stock-based compensation	75.7		75.7
Other comprehensive income	(0.6)				(0.6)
Net income (loss)	32.7			32.7
Shares outstanding, end of the period (in shares) at Sep. 30, 2020		414.3
Shareholders equity, ending balance at Sep. 30, 2020	$ 851.3	$ 0.0	$ 2,608.8	$ (1,764.3)	$ 6.8