Stock Options (Schedule of Non-Qualified Stock Options Activity) (Details) - Non Qualified Options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares
Options outstanding at beginning of year (in shares)	5,300	40,200	67,000
Granted (in shares)	0	0	0
Exercised (in shares)	(2,300)	(34,900)	(26,800)
Canceled (in shares)	0	0	0
Options outstanding at end of year (in shares)	3,000	5,300	40,200
Exercise Price
Outstanding at beginning of year, exercise price (in dollars per share)	$ 46.87	$ 42.99	$ 42.43
Granted, exercise price (in dollars per share)	0	0	0
Exercised, exercise price (in dollars per share)	38.22	42.40	41.61
Canceled, exercise price (in dollars per share)	0	0	0
Outstanding at end of year, exercise price (in dollars per share)	$ 46.87	$ 42.99	$ 42.43	$ 53.51	$ 46.87	$ 42.99
Options exercisable at end of year (in shares)				3,000	5,300	34,400
Exercisable at end of year, exercise price (in dollars per share)				$ 53.51	$ 46.87	$ 41.21