Stock Options and Incentive Plans (Schedules of Stock Option Activity) (Details) - Stock Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Shares under option	62,390	88,773	187,233
Options canceled	150
Options exercised	32,900	26,383	98,460
Shares under option at December 31	29,340	62,390	88,773
Options exercisable at December 31	29,340	62,390	88,773
Weighted Average Exercise Price
Shares under option January 1	$ 18.28	$ 18.67	$ 18.99
Options canceled	20.63
Options exercised	18.16	19.60	19.27
Shares under option December 31	18.40	18.28	18.67
Options exercisable December 31	$ 18.40	$ 18.28	$ 18.67