CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - UNAUDITED - USD ($) shares in Millions, $ in Millions	Total	Class A and Class B Common Stock	Class A and Class B Common Stock Class A Common Stock	Class A and Class B Common Stock Class B Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Loss
Beginning Balance at Dec. 31, 2019	$ 560.4
Beginning balance (in shares) at Dec. 31, 2019	158.9
Increase (Decrease) in Temporary Equity [Roll Forward]
Tender offer and subsequent conversion (Note 9) (in shares)	2.9
Ending balance (in shares) at Mar. 31, 2020	161.8
Ending Balance at Mar. 31, 2020	$ 560.4
Beginning balance at Dec. 31, 2019	(374.0)	$ 0.0			$ (0.1)	$ 10.5	$ 0.6	$ (385.0)
Beginning balance (in shares) at Dec. 31, 2019			0.0	44.4
Treasury stock, beginning balance (in shares) at Dec. 31, 2019					4.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(105.6)							(105.6)
Changes in other comprehensive income	(1.8)						(1.8)
Tender offer and subsequent conversion (Note 9) (in shares)				(2.9)
Tender offer and subsequent conversion	25.1					25.1
Common stock—option exercises (in shares)				0.4
Common stock—option exercises	0.3					0.3
Common stock—shared-based compensation expense	0.6					0.6
Treasury stock, ending balance (in shares) at Mar. 31, 2020					4.5
Ending balance (in shares) at Mar. 31, 2020			0.0	41.9
Ending balance at Mar. 31, 2020	(455.4)	0.0			$ (0.1)	36.5	(1.2)	(490.6)
Beginning Balance at Dec. 31, 2020	$ 0.0
Beginning balance (in shares) at Dec. 31, 2020	0.0
Ending balance (in shares) at Mar. 31, 2021	0.0
Ending Balance at Mar. 31, 2021	$ 0.0
Beginning balance at Dec. 31, 2020	1,032.4	0.0			$ (0.8)	1,775.6	5.6	(748.0)
Beginning balance (in shares) at Dec. 31, 2020			59.4	192.2
Treasury stock, beginning balance (in shares) at Dec. 31, 2020					4.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(99.6)							(99.6)
Changes in other comprehensive income	(3.5)						(3.5)
Conversion of Class B to Class A (in shares)	$ 0.0		$ 26.1	$ (26.1)
Common stock—option exercises (in shares)	1.2		1.0	0.3
Common stock—option exercises	$ 2.3					2.3
Reclassification of early-exercised stock option to liabilities	0.4					0.4
Common stock—shared-based compensation expense	2.3					2.3
Treasury stock, ending balance (in shares) at Mar. 31, 2021					4.6
Ending balance (in shares) at Mar. 31, 2021			86.5	166.4
Ending balance at Mar. 31, 2021	$ 934.3	$ 0.0			$ (0.8)	$ 1,780.6	$ 2.1	$ (847.6)