Stock Options (Schedule of Non-Qualified Stock Options Activity) (Details) - Non Qualified Options - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Options outstanding at beginning of year (in shares)	67,000	112,400	127,300
Granted (in shares)	0	0	0
Exercised (in shares)	(26,800)	(45,400)	(14,900)
Canceled (in shares)	0	0	0
Options outstanding at end of year (in shares)	40,200	67,000	112,400
Exercise Price
Outstanding at beginning of year, exercise price (in dollars per share)	$ 42.43	$ 34.48	$ 32.05
Granted, exercise price (in dollars per share)	0	0	0
Exercised, exercise price (in dollars per share)	41.61	22.73	13.73
Canceled, exercise price (in dollars per share)	0	0	0
Outstanding at end of year, exercise price (in dollars per share)	$ 42.43	$ 34.48	$ 32.05	$ 42.99	$ 42.43	$ 34.48
Options exercisable at end of year (in shares)				34,400	50,400	85,000
Exercisable at end of year, exercise price (in dollars per share)				$ 41.21	$ 39.86	$ 29.61
Options available for grant at end of year (in shares)				146,075	176,294	207,608