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Stock-Based Compensation Restricted Stock Awards (Details) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Weighted Average Grant Date Fair Value [Abstract]      
Granted $ 61.11    
Restricted Stock [Member]
     
Restricted Stock Shares [Abstract]      
Non-vested at beginning of year 178,904    
Granted 245,355    
Vested (151,912)    
Forfeited (1,623)    
Non-vested at end of year 270,724 178,904  
Weighted Average Grant Date Fair Value [Abstract]      
Granted $ 65.70    
Vested $ 51.60    
Non-vested at beginning of year $ 44.27    
Forfeited $ 51.18    
Non-vested at end of year $ 59.54 $ 44.27  
Weighted average grant date fair value of restricted stock granted during the year $ 65.70 $ 56.03 $ 37.59
Total intrinsic value of restricted stock that vested during year $ 7.8 $ 4.4 $ 2.1