Equity Plans Equity Plans (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 purchase_interval	Dec. 31, 2012	Dec. 31, 2011
Summary of Activity under the Plan [Abstract]
Compensation costs charged to income	$ 912	$ 564	$ 651
Proceeds from the exercise of stock options and similar instruments	1,004	989	564
Tax benefits realized from share options exercised	28	97	7
Employee Stock Purchase Plan [Abstract]
Number of purchases intervals under the plan since inception	15
Shares issued during the period under the plan	30,869	29,468	25,712
Cash received from employees toward purchases under the plan	796	627	548
Restricted Stock and Deferred Restricted Stock [Member]
Summary of Activity under the Plan [Abstract]
Compensation costs charged to income	784	460	559
Tax benefits realized from share options exercised	97	36	7
Employee Stock Purchase Plan [Abstract]
Unrecognized compensation cost	618
Deferred Restricted Stock Awards [Member]
Dividend Equivalent Rights [Abstract]
Cumulative dividend equivalent rights converted to deferred restricted stock awards	61,733	56,349	50,888
Employee Stock Option [Member]
Summary of Activity under the Plan [Abstract]
Proceeds from the exercise of stock options and similar instruments	198	318	0
Tax benefits realized from share options exercised	(69)	61	0
Dividend Equivalent Rights [Member]
Dividend Equivalent Rights [Abstract]
Liability for dividend equivalent rights	128	128	129
Incentive Plan [Member]
Option Indexed to Issuer's Equity [Line Items]
Number of shares reserved for issuance under the plan	1,800,000
Maximum number of shares per employee	600,000
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued Pursuant To The Plan	341,941	287,534	235,473
Shares issuable under the plan upon exercise of outstanding awards	307,919	327,093	363,700
Number of shares available for grant	1,150,167	1,185,373	1,200,827
Dividend Reinvestment and Stock Purchase Plan [Member]
Option Indexed to Issuer's Equity [Line Items]
Number of shares reserved for issuance under the plan	3,000,000
Shares issued under the plan	3,111	3,487	1,679
Summary of Activity under the Plan [Abstract]
Proceeds from the exercise of stock options and similar instruments	84	83	39
Employee Stock [Member]
Option Indexed to Issuer's Equity [Line Items]
Number of shares reserved for issuance under the plan	270,400
Summary of Activity under the Plan [Abstract]
Compensation costs charged to income	128	104	92
Proceeds from the exercise of stock options and similar instruments	722	588	525
Employee Stock Purchase Plan [Abstract]
Purchase price of common stock to employees under the plan, percent	85.00%
Maximum amount of base salary employees can designate for share purchase under the plan	10.00%
Expenses recorded under the plan	140	110	96
Unrecognized compensation cost	$ 65