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Stock Based Compensation (Summary of Stock Option Activity) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Stock-Based Compensation [Abstract]      
Options, Outstanding, beginning of period 194,521 206,463 219,540
Options, Granted 16,000 14,500 12,500
Options, Exercised (30,823) (16,859) (25,577)
Options, Forfeited (19,269) (9,583)  
Options, Outstanding, end of period 160,429 194,521 206,463
Options, Exercisable, end of period 144,429 180,021 193,963
Weighted Average Exercise Price Per Share, Outstanding, beginning of period $ 26.91 $ 26.74 $ 26.64
Weighted Average Exercise Price Per Share, Granted 33.56 28.55 29.08
Weighted Average Exercise Price Per Share, Exercised 27.34 26.19 27.05
Weighted Average Exercise Price Per Share, Forfeited 27.86 27.02  
Weighted Average Exercise Price Per Share, Outstanding, end of period 27.37 26.91 26.74
Weighted Average Exercise Price Per Share, Exercisable, end of period $ 26.39 $ 26.78 $ 26.59
Weighted Average Remaining Contractual Term, Outstanding 5 years 7 months 6 days    
Aggregate Intrinsic Value, Outstanding, beginning of period $ 362,754 $ 477,640  
Aggregate Intrinsic Value, Outstanding, end of period 931,963 362,754 $ 477,640
Aggregate Intrinsic Value, Exercisable at end of period $ 931,963 $ 359,854 $ 477,640