Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 37.6	$ 1.5	$ 104.5	$ 62.2
Weighted average common shares outstanding (in shares)	73,300,000	72,200,000	73,000,000	71,900,000
Dilutive effect of stock options, stock appreciation rights and performance share awards, based on the treasury stock method (in shares)	1,700,000	1,700,000	1,700,000	1,700,000
Weighted average shares assuming dilution (in shares)	75,000,000	73,900,000	74,700,000	73,600,000
Antidilutive options excluded from computation of diluted net income per share (in shares)	100,000	800,000	100,000	600,000
Stock repurchase program, shares authorized	700,000		700,000
Stock repurchase program, shares purchased	117,310		370,810
Stock repurchase program, cost of shares purchased	$ 9.6		$ 26.8
Stock repurchase program, average price per share	$ 81.46		$ 72.14