Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income, as reported, for basic net income per share	$ 241.7	$ 206.9	$ 150.7
Weighted average common shares outstanding (in shares)	74,000,000.0	73,900,000	73,900,000
Assumed stock options exercised and awards vested, based on the treasury stock method (in shares)	1,400,000	1,500,000	1,900,000
Weighted average shares assuming dilution (in shares)	75,400,000	75,400,000	75,800,000
Antidilutive options excluded from computation of diluted net income per share (in shares)	100,000	400,000	400,000
Share repurchase program, number of shares authorized	848,000	800,000
Shares purchased under share repurchase program (in shares)	800,000
Shares purchased under share repurchase program	$ 83.1	$ 70.8	$ 74.4
Shares purchased under share repurchase program, average cost per share	$ 103.89