Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 60.9	$ 22.1
Weighted average common shares outstanding (in shares)	73,300,000	72,500,000
Dilutive effect of stock options, stock appreciation rights and performance share awards, based on the treasury stock method (in shares)	1,600,000	1,600,000
Weighted average shares assuming dilution (in shares)	74,900,000	74,100,000
Antidilutive options excluded from computation of diluted net income per share (in shares)	200,000	600,000
Stock repurchase program, shares authorized			800,000
Stock repurchase program, shares purchased	325,000
Stock repurchase program, cost of shares purchased	$ 26.9
Stock repurchase program, average price per share	$ 82.84