Equity Plans (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		0 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Incentive Plan [Member]	Jun. 30, 2014 Employee Stock Purchase Plan (ESPP) [Member]	Jun. 30, 2013 Employee Stock Purchase Plan (ESPP) [Member]	Jun. 30, 2014 Employee Stock Purchase Plan (ESPP) [Member]	Jun. 30, 2013 Employee Stock Purchase Plan (ESPP) [Member]	Jun. 30, 2014 2014 Employee Stock Purchase Plan [Member]	Jun. 30, 2014 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Jun. 30, 2013 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Jun. 30, 2014 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Jun. 30, 2013 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Jun. 30, 2014 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2013 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2014 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2013 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2014 Stock Options [Member]	Jun. 30, 2013 Stock Options [Member]	Jun. 30, 2014 Stock Options [Member]	Jun. 30, 2013 Stock Options [Member]	Apr. 30, 2014 Restricted Stock Units (RSUs) [Member]	Jan. 31, 2014 Restricted Stock Units (RSUs) [Member] vesting_installment	Jan. 02, 2014 Restricted Stock Units (RSUs) [Member] vesting_installment	Jun. 30, 2014 Common Stock [Member] Employee Stock Purchase Plan (ESPP) [Member]	Jun. 30, 2014 Dividend Equivalent Rights [Member]	Jun. 30, 2013 Dividend Equivalent Rights [Member]	Jun. 30, 2014 Dividend Equivalent Rights [Member]	Jun. 30, 2013 Dividend Equivalent Rights [Member]	Apr. 14, 2014 Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining shares available for issuance under the Incentive Plan					1,110,805
Shares issuable upon exercise of Incentive Plan awards					309,516
Compensation costs charged to income:	$ 207,000	$ 242,000	$ 451,000	$ 589,000		$ 0	$ 0	$ 72,000	$ 58,000						$ 207,000	$ 242,000	$ 379,000	$ 531,000
Excess tax benefits realized from share options exercised and stock issuance	251,000	65,000	309,000	95,000											251,000	65,000	250,000	95,000	0	0	59,000	0
Proceeds from the exercise of stock options and similar instruments	8,000	21,000	484,000	366,000		0	0	406,000	328,000		8,000	21,000	34,000	38,000					0	0	44,000	0
Unrecognized compensation costs						13,000		13,000							1,163,000		1,163,000		0		0
Recognition period for unrecognized compensation cost																	1 year 2 months 19 days
Number of equity instruments granted																							9,002	3,845	21,790
Number of equal successive installments for vesting of stock awards																								3	3
Grant date fair value of equity instruments granted																							$ 26.48	$ 26.39	$ 26.80
Liability accrued for Dividend Equivalent Rights																											29,000	31,000	62,000	65,000
Decrease to retained earnings for compensation cost related to Dividend Equivalent Rights																											29,000	31,000	62,000	65,000
Purchase price of common stock under ESPP, percent								85.00%
Maximum percentage of base compensation employees can designate for stock purchases under ESPP						10.00%		10.00%
Number of shares authorized for issuance under the plan										400,000	3,000,000		3,000,000													270,400
Plan expense						$ 39,000	$ 37,000	$ 75,000	$ 58,000
Number of shares issued under the DRSPP											276	825	1,151	1,444
Shares Deregistered (in shares)																															2,993,744