Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance under the 2011 Plan (in shares)	2,639,265		2,639,265
Stock options, granted (in shares)			905,028
Stock options, weighted average exercise price (in dollars per share)			$ 55.63
Stock options, weighted average grant date fair value (in dollars per share)			$ 10.50
Assumptions used in Black-Scholes model
Risk-free interest rate (in hundredths)			1.61%
Expected life (in years)			5 years 10 months
Stock volatility (in hundredths)			19.20%
Dividend yield (in hundredths)			0.90%
Stock-based compensation expense	$ 3.6	$ 3.6	$ 24.4	$ 12.5
Stock-based compensation expense, executive retirements			$ 10.4
Performance Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			140,369
Grant date fair value (in dollars per share)			$ 55.26
Performance period			3 years
Number of shares of common stock per PVS award (in shares)	1		1
PVS payout, Minimum (in hundredths)	0.00%		0.00%
PVS payout, Maximum (in hundredths)	200.00%		200.00%
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			30,499
Grant date fair value (in dollars per share)			$ 57.38