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Stock-Based Compensation (Summary of Stock Option Activity) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Stock Based Compensation [Abstract]    
Options, beginning of year 212,725 225,669
Options, Granted 28,900 34,750
Options, Exercised (28,275) (44,219)
Options, Forfeited (4,650) (3,475)
Options, end of year 208,700 212,725
Options, Exercisable, end of period 179,800 177,975
Weighted Average Exercise Price Per Share, Outstanding, beginning of period $ 20.76 $ 19.46
Weighted Average Exercise Price Per Share, Granted 32.34 32.81
Weighted Average Exercise Price Per Share, Exercised 18.39 23.53
Weighted Average Exercise Price Per Share, Forfeited 27.08 21.71
Weighted Average Exercise Price Per Share, Outstanding, end of period 22.54 20.76
Weighted Average Exercise Price Per Share, Exercisable, end of period $ 20.97 $ 18.41
Weighted Average Remaining Contractual Term, Outstanding 5 years 10 months 24 days  
Aggregate Intrinsic Value, Outstanding, beginning of period $ 2,604,097  
Aggregate Intrinsic Value, Outstanding, end of period 2,182,537 $ 2,604,097
Aggregate Intrinsic Value, Exercisable at end of period $ 2,163,463 $ 2,597,494