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Stock-Based Compensation (Details 3) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Weighted Average Grant Date Fair Value [Abstract]      
Granted $ 55.78    
Restricted Stock [Member]
     
Restricted Stock Shares [Abstract]      
Non-vested at beginning of year 187,436    
Granted 77,152    
Vested (82,345)    
Forfeited (3,339)    
Non-vested at end of year 178,904 187,436  
Weighted Average Grant Date Fair Value [Abstract]      
Non-vested at beginning of year $ 35.31    
Granted $ 56.03    
Vested $ 35.08    
Forfeited $ 39.47    
Non-vested at end of year $ 44.27 $ 35.31  
Weighted average grant date fair value of restricted stock granted during the year $ 56.03 $ 37.59 $ 27.42
Total intrinsic value of restricted stock that vested during year $ 4.4 $ 2.1 $ 1.8