Income Taxes (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, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current tax expense
Federal													$ 11,895	$ 9,748	$ 10,010
State													672	511	611
Total current tax expense													12,567	10,259	10,621
Deferred tax benefit
Federal													(2,800)	(1,934)	(1,502)
State													(133)	(134)	(54)
Total deferred tax benefit													(2,933)	(2,068)	(1,556)
Total income tax expense	2,265	2,388	2,499	2,482	1,076	2,472	2,441	2,202	2,073	2,507	2,149	2,336	9,634	8,191	9,065
Components of income tax expense (benefit) recorded directly to stockholders' equity
Unrealized (loss) gain on securities available for sale													(24)	1,362	580
Reclassification adjustment for securities gains realized in income															(56)
Compensation expense for tax purposes in excess of amounts recognized for financial reporting purposes													(83)	(125)	(140)
Minimum Pension Liability adjustment													2	(111)	(17)
Total income tax (benefit) expense recorded directly to stockholders' equity													$ (105)	$ 1,126	$ 367