Stock and Other Incentive Plans (Details 1) - Employee Stock Purchase Plan [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Options Outstanding:
Options outstanding, beginning of year (shares)	316,321	340,958	393,902
Granted (shares)	206,824	198,450	197,640
Exercised (shares)	(32,076)	(57,924)	(44,462)
Forfeited (shares)	(40,659)	(22,081)	(47,176)
Expired (shares)	(132,310)	(143,082)	(158,946)
Outstanding, end of period (shares)	318,100	316,321	340,958
Exercisable, end of period (shares)	318,100	316,321	340,958
Weighted-average exercise price:
Options outstanding, beginning of year (in USD per share)	$ 23.69	$ 20.70	$ 19.17
Options granted during the year (in USD per share)	25.77	24.07	23.22
Options exercised during the year (in USD per share)	24.31	21.40	19.41
Options forfeited during the year (in USD per share)	25.01	23.16	19.90
Options expired during the year (in USD per share)	23.22	18.11	20.41
Options outstanding, end of year (in USD per share)	25.00	23.69	20.70
Weighted-average fair value of options granted during the year (calculated as of the grant date) (in USD per share)	$ 6.31	$ 5.37	$ 5.39
Intrinsic value of options exercised during the year	$ 271,000	$ 634,000	$ 381,000
Intrinsic value of options outstanding (calculated as of December 31)	2,683,000	2,098,000	2,597,000
Intrinsic value of options exercisable (calculated as of December 31)	$ 2,682,519	$ 2,097,898	$ 2,597,238
Exercise prices of options outstanding (calculated as of December 31) (in USD per share)	$ 25.00	$ 23.69	$ 20.70
Weighted-average contractual life of outstanding options (calculated as of December 31, in years)	9 months 18 days	9 months 18 days	9 months 18 days