Income Taxes (Reconciliation of Expected Income Tax Benefit Computed Using Federal Statutory Income Tax Rate) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Computed tax expense									$ 12,008	$ 13,285	$ 12,558
Tax exempt income									(623)	(753)	(888)
State taxes, net of federal benefit									297	301	281
Income from life insurance									(484)	(760)	(517)
Low income housing credits									(328)	(393)	(381)
Other									12	101	60
Income tax expense	$ 1,904	$ 2,992	$ 2,894	$ 3,092	$ 2,536	$ 3,054	$ 3,257	$ 2,934	$ 10,882	$ 11,781	$ 11,113
Income tax rate used for calculations									35.00%	35.00%	35.00%