Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Income taxes    
Valuation allowance $ 0 $ 0
Unrecognized tax benefits 7.9 7.9
Unrecognized Tax Benefits that Would Impact Effective Tax Rate 1.6 1.6
State    
Income taxes    
Net operating loss resulting from repairs and maintenance deductions 49.9 49.9
Federal    
Income taxes    
Net operating loss resulting from repairs and maintenance deductions $ 43.8 $ 43.8