Shareholder's Equity - Change in Shareholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,490.2	$ 1,573.2	$ 1,369.5	$ 1,396.3	$ 1,573.2	$ 1,396.3
Net income	91.2	74.3	66.1	55.4	$ 165.5	121.5
Activity related to stock-based compensation	$ 20.4	12.8	19.7	10.7
Share purchased under share repurchase program (in shares)	0				(761,500)
Shares purchased under share repurchase program		(115.5)		(83.1)	$ (115.5)
Dividends declared		(11.8)	(11.4)	(10.6)
Other comprehensive income (loss), net of tax	$ 4.5	(42.7)	1.2	0.8	(38.2)	2.0
Balance	$ 1,606.3	1,490.2	$ 1,445.1	$ 1,369.5	1,606.3	$ 1,445.1
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		$ (0.1)			$ (0.1)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000
Balance	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8
Balance (in shares)	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000	75,300,000
Balance	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8	$ 18.8
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	267.6	272.7	278.5	282.0	272.7	282.0
Activity related to stock-based compensation	(4.5)	(5.1)	(5.1)	(3.5)
Balance	$ 263.1	$ 267.6	$ 273.4	$ 278.5	$ 263.1	$ 273.4
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)	1,700,000	1,200,000	1,800,000	1,200,000	1,200,000	1,200,000
Balance	$ (215.7)	$ (118.1)	$ (172.6)	$ (103.7)	$ (118.1)	$ (103.7)
Activity related to stock-based compensation	$ 24.9	$ 17.9	$ 24.8	$ 14.2
Activity related to stock -based compensation (in shares)	(200,000)	(300,000)	(200,000)	(200,000)
Share purchased under share repurchase program (in shares)		800,000		800,000
Shares purchased under share repurchase program		$ (115.5)		$ (83.1)
Balance (in shares)	1,500,000	1,700,000	1,600,000	1,800,000	1,500,000	1,600,000
Balance	$ (190.8)	$ (215.7)	$ (147.8)	$ (172.6)	$ (190.8)	$ (147.8)
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	1,611.8	1,549.4	1,398.2	1,353.4	1,549.4	1,353.4
Net income	91.2	74.3	66.1	55.4
Dividends declared		(11.8)	(11.4)	(10.6)
Balance	1,703.0	1,611.8	1,452.9	1,398.2	1,703.0	1,452.9
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		(0.1)			(0.1)
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(192.3)	(149.6)	(153.4)	(154.2)	(149.6)	(154.2)
Other comprehensive income (loss), net of tax	4.5	(42.7)	1.2	0.8
Balance	$ (187.8)	$ (192.3)	$ (152.2)	$ (153.4)	$ (187.8)	$ (152.2)