Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock Class A	Common Stock Class B	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Balance (in shares) at Dec. 31, 2018		22.0	1.0
Balance at Dec. 31, 2018	$ 1,197.2	$ 0.0	$ 0.1	$ 35.0	$ 0.0	$ 1,162.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56.4					56.4
Loss on cash flow hedges, net of tax benefit	0.0
Issuance of stock in connection with employee stock plans	2.3	$ 2.3
Issuance of restricted stock to employees (in shares)		0.1
Issuance of restricted stock to employees	0.0	$ 0.0
Repurchase of Class A common stock (in shares)		0.0
Repurchase of Class A common stock	(3.1)	$ (3.1)
Class B common stock converted to Class A common stock (in shares)		0.2	(0.2)
Class B common stock converted to Class A common stock	0.0
Compensation for stock and stock option issuances and excess tax benefits from option exercises	3.5	$ 10.5		(7.0)
Dividends paid	(6.7)					(6.7)
Balance (in shares) at Mar. 31, 2019		22.3	0.8
Balance at Mar. 31, 2019	1,250.5	$ 9.7	$ 0.1	28.0	0.0	1,212.7
Balance (in shares) at Dec. 31, 2019		22.6	0.6
Balance at Dec. 31, 2019	1,467.7	$ 20.5	$ 0.1	46.0	(0.7)	1,401.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46.2					46.2
Loss on cash flow hedges, net of tax benefit	(5.1)				(5.1)
Issuance of stock in connection with employee stock plans (in shares)		0.0
Issuance of stock in connection with employee stock plans	2.6	$ 2.6
Issuance of restricted stock to employees (in shares)		0.1
Issuance of restricted stock to employees	0.0	$ 0.0
Repurchase of Class A common stock (in shares)		(0.5)
Repurchase of Class A common stock	(48.2)	$ (32.0)		(16.2)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	5.1	$ 8.9		(3.8)
Dividends paid	(7.0)					(7.0)
Balance (in shares) at Mar. 31, 2020		22.2	0.6
Balance at Mar. 31, 2020	$ 1,456.5	$ 0.0	$ 0.1	$ 26.0	$ (5.8)	$ 1,436.2