Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Analysis of the difference between the statutory and effective tax rates from operations
U.S. federal income tax rate (as a percent)	35.00%	35.00%	35.00%
Tax exempt interest income (as a percent)	(3.80%)	(3.70%)	(3.30%)
Tax credits (as a percent)	(2.20%)	(2.60%)	(2.50%)
Cash surrender value of life insurance (as a percent)	(1.90%)	(1.50%)	(2.00%)
State income taxes (as a percent)	1.00%	0.90%	1.10%
Establish deferred taxes on tax credit investments (as a percent)		(2.20%)
Other, net (as a percent)	(0.90%)	(0.10%)
Effective tax rate (as a percent)	27.20%	25.80%	28.30%
Adjustment to deferred tax assets that relates to tax-advantaged investments		$ 700,000
Deferred tax assets and deferred tax liabilities
Allowance for loan loss	11,495,000	10,724,000
Deferred compensation	3,950,000	3,363,000
Accrued expenses	1,451,000	412,000
Investments in partnerships	713,000	749,000
Write-downs and costs associated with other real estate owned	1,335,000	573,000
Other assets	847,000	847,000
Total deferred tax assets	19,791,000	16,668,000
Securities	4,088,000	4,101,000
Property and equipment	1,162,000	1,213,000
Loan costs	648,000	592,000
Prepayment penalty on modification of FHLB advances	263,000	369,000
Mortgage servicing rights	703,000	538,000
Other liabilities	389,000	274,000
Total deferred tax liabilities	7,253,000	7,087,000
Net deferred tax asset	$ 12,538,000	$ 9,581,000