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Stock-Based Compensation (Details 2) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Summary of stock award activity      
Unvested Shares, Beginning Balance 271,624    
Unvested Weighted average grant date fair value, Beginning Balance $ 29.11    
Granted, Shares 118,916    
Granted, Weighted average grant date fair value $ 41.00 $ 35.79 $ 24.10
Vested, Shares (61,051)    
Vested, Weighted average grant date fair value $ 24.18    
Forfeited, Shares (86,633)    
Forfeited, Weighted average grant date fair value $ 24.48    
Unvested Shares, Ending Balance 242,856 271,624  
Unvested Weighted average grant date fair value, Ending Balance $ 37.83 $ 29.11