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)
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Release of restricted stock units (in shares)		2.6
Shares repurchased for tax withholdings on release of restricted stock (in shares)		(1.0)
Shares repurchased for tax withholdings on release of restricted stock	(25.5)		(17.0)	(8.5)
Exercise of stock options and awards (in shares)		0.2
Exercise of stock options and awards	0.9		0.9
Assumed stock options in connection with acquisition	0.8		0.8
Stock-based compensation	55.6		55.6
Other comprehensive income (loss)	3.0				3.0
Net income (loss)	(7.7)
Shares outstanding, end of the period (in shares) at Mar. 31, 2019		411.4
Shareholders equity, ending balance at Mar. 31, 2019	704.9	$ 0.0	2,377.8	(1,674.7)	1.8
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 (in shares)		2.7
Shares repurchased for tax withholdings on release of restricted stock (in shares)	(1.0)	(1.0)
Shares repurchased for tax withholdings on release of restricted stock	$ (18.9)		(9.3)	(9.6)
Repurchases of common stock (in shares)		(3.7)
Repurchases of common stock	$ (64.0)		(33.9)	(30.1)
Exercise of stock options and awards (in shares)	0.1	0.1
Exercise of stock options and awards	$ 0.6		0.6
Stock-based compensation	39.8		39.8
Other comprehensive income (loss)	(4.8)				(4.8)
Net income (loss)	39.3
Shares outstanding, end of the period (in shares) at Mar. 31, 2020		415.1
Shareholders equity, ending balance at Mar. 31, 2020	$ 800.4	$ 0.0	$ 2,528.5	$ (1,726.6)	$ (1.5)