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		0 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Incentive Plan [Member]	Jun. 30, 2012 ESPP [Member]	Jun. 30, 2011 ESPP [Member]	Jun. 30, 2012 ESPP [Member]	Jun. 30, 2011 ESPP [Member]	Jun. 30, 2012 Dividend Reinvestment and Stock Purchase Plan [Member]	Jun. 30, 2011 Dividend Reinvestment and Stock Purchase Plan [Member]	Jun. 30, 2012 Dividend Reinvestment and Stock Purchase Plan [Member]	Jun. 30, 2011 Dividend Reinvestment and Stock Purchase Plan [Member]	Jun. 30, 2012 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2011 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2012 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2011 Restricted Stock and Deferred Restricted Stock [Member]	Jun. 30, 2012 Employee Stock Option [Member]	Jun. 30, 2011 Employee Stock Option [Member]	Jun. 30, 2012 Employee Stock Option [Member]	Jun. 30, 2011 Employee Stock Option [Member]	Jan. 24, 2012 Restricted Stock Units (RSUs) [Member] Y	Jan. 03, 2012 Restricted Stock Units (RSUs) [Member]	Jan. 24, 2012 Market Performance-vesting Restricted Stock Units [Member]	Jun. 30, 2012 Dividend Equivalent Rights [Member]	Jun. 30, 2011 Dividend Equivalent Rights [Member]	Jun. 30, 2012 Dividend Equivalent Rights [Member]	Jun. 30, 2011 Dividend Equivalent Rights [Member]	Apr. 25, 2012 Non-Employee Board Member [Member] members	Apr. 25, 2012 Non-Employee Board Member [Member] Common Stock [Member] Restricted Stock and Deferred Restricted Stock [Member]	Apr. 25, 2012 Non-Employee Board Member [Member] Common Stock [Member] Dividend Equivalent Rights [Member]	May 25, 2012 Key Executive [Member] Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining shares available for issuance under the Incentive Plan					1,185,373
Shares issuable upon exercise of Incentive Plan awards					344,196
Compensation costs charged to income	$ 100,000	$ 126,000	$ 283,000	$ 328,000		$ 0	$ 0	$ 49,000	$ 45,000					$ 100,000	$ 126,000	$ 234,000	$ 283,000
Excess tax benefits realized from share options exercised and stock issuance	43,000	0	43,000	7,000										35,000	0	35,000	7,000	8,000	0	8,000	0
Proceeds from the exercise of stock options and similar instruments	96,000	8,000	405,000	262,000		0	0	278,000	254,000	21,000	8,000	52,000	8,000					75,000	0	75,000	0
Number of equity instruments granted																						4,321	17,670
Grant date fair value of equity instruments granted																						$ 21.02	$ 21.92
Number of equal successive installments for vesting of stock awards																						3
Number of equity instruments forfeited																								7,000								4,998
Number of retiring board members																													2
Shares issued in period																														9,832	2,199
Reversal of share-based compensation			(283,000)	(328,000)																												12,000
Requisite service period for market performance restricted stock units																								3 years
Unrecognized compensation costs						9,000		9,000						848,000		848,000
Unrecognized compensation costs, period for recognition																2 years 2 months 23 days
Liability accrued for Dividend Equivalent Rights																									32,000	32,000	66,000	64,000
Decrease to retained earnings for compensation cost related to Dividend Equivalent Rights																									32,000	32,000	66,000	64,000
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						270,400		270,400		3,000,000		3,000,000
Plan expense						$ 28,000	$ 25,000	$ 45,000	$ 40,000
Number of shares issued under the DRSPP										896	349	2,198	349