Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefit	$ 1.0		$ 1.0
Stock-Based Compensation Activity
Maximum payout range	170.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	3.7		2.6
Total Shareholder Return [Member]
Stock-Based Compensation Activity
Number of shares granted	207,880
Fair value of shares granted	$ 34.68
Equity Instruments Other than Options, Converted in Period	355,233	[1]
Performance Units Related to Earnings Per Share [Member]
Stock-Based Compensation Activity
Number of shares granted	69,295
Fair value of shares granted	$ 34.69
Equity Instruments Other than Options, Converted in Period	118,404	[1]
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	0.1		0.1
Stock-Based Compensation Activity
Number of shares granted	1,164
Fair value of shares granted	$ 35.56
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	3.8		2.7
Less: Amount paid by unconsolidated affiliates	1.2		0
Net compensation expense	2.6		2.7
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	495,185
Restricted Stock [Member]
Stock-Based Compensation Activity
Shares Paid for Tax Withholding for Share Based Compensation	1,411
Total Shareholder Return [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	2.0		2.0
Performance Units Related to Earnings Per Share [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 1.7		$ 0.6

[1] Performance units were converted based on a payout ratio of 170 percent of the target number of performance units granted in February 2011 and are included in the 495,185 shares of common stock issued during the three months ended March 31, 2014 as discussed above.