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Share-Based Compensation Plan (Textual) (Details) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Share-Based Compensation Plans (Textual) [Abstract]      
Share-based compensation expense $ 2,854,000 $ 1,865,000 $ 1,517,000
Common stock available for future grants under share-based compensation plans 673,801    
Stock option vesting period, 2013 grants 5 years    
Stock option vesting period pre 2013 grants 3 years    
Stock Options and Restricted Stock Performance Units [Member]
     
Share-Based Compensation Plans (Textual) [Abstract]      
Share-based compensation expense 2,900,000 1,900,000 1,500,000
Stock Options [Member]
     
Share-Based Compensation Plans (Textual) [Abstract]      
Corporation granted options to purchase common stock 244,719    
Stock option expiration period 10 years    
Intrinsic value of outstanding in-the-money stock options 6,300,000    
Intrinsic value of exercisable in-the-money stock options 3,200,000    
Closing price of common stock $ 31.67    
Unrecognized compensation expense related to share-based compensation 2,100,000    
Period of common stock historical volatility 7 years    
Equity Option [Member]
     
Share-Based Compensation Plans (Textual) [Abstract]      
Unrecognized Compensation, Stock Options, Total Compensation Cost Not yet Recognized, Period for Recognition 3 years    
Restricted Stock Units (RSUs) [Member]
     
Share-Based Compensation Plans (Textual) [Abstract]      
Corporation granted options to purchase restricted stock performance units 71,768 69,772 52,087
Unrecognized compensation expense related to share-based compensation $ 2,300,000    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 2 years    
Restricted Stock Units (RSUs) [Member] | Maximum [Member]
     
Share-Based Compensation Plans (Textual) [Abstract]      
Restricted stock performance units eligible to vest as a multiple of number of units granted 1.5    
Restricted Stock Units (RSUs) [Member] | Minimum [Member]
     
Share-Based Compensation Plans (Textual) [Abstract]      
Restricted stock performance units eligible to vest as a multiple of number of units granted 0.25