Equity Plans (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		0 Months Ended			3 Months Ended		9 Months Ended		0 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Incentive Plan [Member]	Sep. 30, 2012 Employee Stock Purchase Plan (ESPP) [Member]	Sep. 30, 2011 Employee Stock Purchase Plan (ESPP) [Member]	Sep. 30, 2012 Employee Stock Purchase Plan (ESPP) [Member]	Sep. 30, 2011 Employee Stock Purchase Plan (ESPP) [Member]	Sep. 30, 2012 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Sep. 30, 2011 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Sep. 30, 2012 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Sep. 30, 2011 Dividend Reinvestment and Stock Purchase Plan (DRSPP) [Member]	Sep. 30, 2012 Restricted Stock and Deferred Restricted Stock [Member]	Sep. 30, 2011 Restricted Stock and Deferred Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock and Deferred Restricted Stock [Member]	Sep. 30, 2011 Restricted Stock and Deferred Restricted Stock [Member]	Sep. 30, 2012 Stock Options [Member]	Sep. 30, 2011 Stock Options [Member]	Sep. 30, 2012 Stock Options [Member]	Sep. 30, 2011 Stock Options [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]	Sep. 30, 2012 Dividend Equivalent Rights [Member]	Sep. 30, 2011 Dividend Equivalent Rights [Member]	Sep. 30, 2012 Dividend Equivalent Rights [Member]	Sep. 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	$ 168,000	$ 185,000	$ 451,000	$ 513,000		$ 55,000	$ 47,000	$ 104,000	$ 92,000					$ 113,000	$ 138,000	$ 347,000	$ 421,000
Excess tax benefits realized from share options exercised and stock issuance	0	0	43,000	7,000										0	0	35,000	7,000	0	0	8,000	0
Proceeds from the exercise of stock options and similar instruments	326,000	285,000	731,000	547,000		310,000	271,000	588,000	525,000	16,000	14,000	68,000	22,000					0	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			(451,000)	(513,000)																												12,000
Requisite service period for market performance restricted stock units																								3 years
Unrecognized compensation costs						35,000		35,000						735,000		735,000
Unrecognized compensation costs, period for recognition																1 year 7 months 21 days
Liability accrued for Dividend Equivalent Rights																									32,000	32,000	98,000	96,000
Decrease to retained earnings for compensation cost related to Dividend Equivalent Rights																									32,000	32,000	98,000	96,000
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						$ 17,000	$ 15,000	$ 62,000	$ 55,000
Number of shares issued under the DRSPP										636	613	2,834	962