Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Performance Shares [Member]	Jun. 30, 2011 Performance Shares [Member]	Jun. 30, 2012 Performance Shares [Member]	Jun. 30, 2011 Performance Shares [Member]	Jun. 30, 2012 Restricted Stock [Member]	Jun. 30, 2011 Restricted Stock [Member]	Jun. 30, 2012 Restricted Stock [Member]	Jun. 30, 2011 Restricted Stock [Member]	Jun. 30, 2012 Stock Compensation Plan [Member]	Jun. 30, 2011 Stock Compensation Plan [Member]	Jun. 30, 2012 Stock Compensation Plan [Member]	Jun. 30, 2011 Stock Compensation Plan [Member]	Jun. 30, 2012 Common Stock	Jun. 30, 2012 Common Stock	Jun. 30, 2012 Restricted Stock [Member]	Jun. 30, 2012 Restricted Stock [Member]	Mar. 31, 2012 Treasury Stock [Member]	Dec. 31, 2011 Treasury Stock [Member]	Jun. 30, 2012 Total Shareholder Return [Member] Performance Shares [Member]	Jun. 30, 2011 Total Shareholder Return [Member] Performance Shares [Member]	Jun. 30, 2012 Total Shareholder Return [Member] Performance Shares [Member]	Jun. 30, 2011 Total Shareholder Return [Member] Performance Shares [Member]	Jun. 30, 2012 Performance Units Related to Earnings Per Share [Member] Performance Shares [Member]	Jun. 30, 2011 Performance Units Related to Earnings Per Share [Member] Performance Shares [Member]	Jun. 30, 2012 Performance Units Related to Earnings Per Share [Member] Performance Shares [Member]	Jun. 30, 2011 Performance Units Related to Earnings Per Share [Member] Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					$ 2.6	$ 2.7	$ 5.1	$ 6.7	$ 0.2	$ 0.2	$ 0.4	$ 0.5	$ 2.8	$ 2.9	$ 5.5	$ 7.2							$ 2.0	$ 1.9	$ 3.8	$ 3.7	$ 0.6	$ 0.8	$ 1.3	$ 3.0
Income tax benefit	1.1	1.1	2.2	2.8
Stock-Based Compensation Activity
Number of shares granted									358
Fair value of shares granted									$ 51.73
Number of shares issued																	4,113	392,700
Treasury stock shares acquired																						120,000
Treasury stock shares reissued																					114,949
Shares issued during period to satisfy restricted stock grants (net of forfeitures)									2,419
Shares Paid for Tax Withholding for Share Based Compensation																			2,587	2,932
Cash Received from Exercise of Stock Options	0.1		0.1
Tax Benefit Realized from Exercise of Stock Options	$ 0		$ 0