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Stock Options (Schedule of Qualified Stock Option Activity) (Details) - Qualified Stock Options - $ / shares
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Shares      
Options outstanding at beginning of year (in shares) 172,875 220,820 254,195
Granted (in shares) 9,500 10,750 21,000
Exercised (in shares) (41,205) (54,945) (43,775)
Canceled (in shares) (1,000) (3,750) (10,600)
Options outstanding at end of year (in shares) 140,170 172,875 220,820
Exercise Price      
Outstanding at beginning of year, exercise price (in dollars per share) $ 43.91 $ 37.39 $ 34.64
Granted, exercise price (in dollars per share) 92.50 83.99 54.87
Exercised, exercise price (in dollars per share) 34.89 24.83 26.59
Canceled, exercise price (in dollars per share) 54.49 54.57 50.68
Outstanding at end of year, exercise price (in dollars per share) $ 49.78 $ 43.91 $ 37.39
Options exercisable at end of year (in shares) 96,320 111,875 136,220
Exercisable at end of year, exercise price (in dollars per share) $ 41.56 $ 36.44 $ 29.66
Options available for grant at end of year (in shares) 336,450 344,950 353,450