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Share-Based Compensation (Nonvested Restricted Stock Activity) (Details) (Restricted Stock and Restricted Stock Units (RSUs) [Member], USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Restricted Stock and Restricted Stock Units (RSUs) [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at December 31, 2010, shares 668,800    
Outstanding at December 31, 2010, weighted average grant date fair value $ 31.16    
Granted, shates 198,800    
Granted, weighted average grant date fair value $ 39.94 $ 24.75 $ 19.13
Vested, shares (67,600)    
Vested, weighted average grant date fair value $ 37.43    
Forfeited, shares (13,300)    
Forfeited, weighted average grant date fair value $ 29.96    
Outstanding at December 31, 2011, shares 786,700 668,800  
Outstanding at December 31, 2011, weighted average grant date fair value $ 32.86 $ 31.16