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Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Mar. 31, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Income Taxes [Abstract]            
Effective tax rate (in hundredths) 32.70%   22.50% 28.40% 23.70%  
Discrete tax charge   $ 0.3     $ 0.2  
Estimated reduction of unrecognized tax benefits 0.3     0.3    
Accrued interest and penalties $ 0.5     $ 0.5   $ 0.4