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Stock-Based Compensation Plans (Tables)
9 Months Ended
Sep. 30, 2011
Stock-Based Compensation Plans [Abstract] 
Information regarding Restricted Shares
                 
          Nine Months Ended September 30, 2011        
            Weighted Average  
            Grant-Date Fair  
    Shares         Value  
Number of unvested shares:
               
Outstanding - January 1, 2011
    1,259,377       $ 77.05  
Granted
    216,644       130.51  
Vested
    (394,849 )      88.73  
Cancelled
    (49,742 )      84.52  
 
           
Outstanding - September 30, 2011
    1,031,430       $ 83.45