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Share-Based Compensation (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Stock-based compensation expense $ 1,707 $ 1,690
Total income tax benefit recognized 708 612
Restricted shares
   
Share-based Compensation Arrangement by Share-based Payment Award    
Shares granted 17,504  
Weighted-average grant date fair value (in dollars per share) $ 47.02  
Vesting period of new awards granted (in years) 3 years  
Fair value of shares vested $ 503 $ 293