Fair Market Value of Financial Assets and Liabilities, Estimated Fair Value Of Financial Instruments and Indication of Level Within Fair Value Hierarachy of Valuation Techniques (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financial assets: [Abstract]
Securities available-for-sale	$ 677,510	$ 603,343
Mortgage servicing rights	2,652	2,364
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets: [Abstract]
Cash and cash equivalents	167,944	207,560
Certificates of deposits in other banks	0	0
Securities available-for-sale	55,329	45,626
Securities held-to-maturity	0	0
Loans held for sale	1,495	22,960
Loans, net	0	0
Federal Home Loan Bank stock	0	0
Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Financial liabilities: [Abstract]
Deposits	619,819	606,448
Repurchase agreements	0	0
Federal funds purchased	0	0
Advances from Federal Home Loan Bank	0	0
Long-term debt	0	0
Accrued interest payable	0	0
Unrecognized financial instruments: [Abstract]
Letters of credit	0	0
Commitments to extend credit	0	0
Forward sale commitments	0	0
Significant Other Observable Inputs (Level 2) [Member]
Financial assets: [Abstract]
Cash and cash equivalents	0	0
Certificates of deposits in other banks	9,335	5,370
Securities available-for-sale	622,181	557,717
Securities held-to-maturity	1,656	1,659
Loans held for sale	0	0
Loans, net	0	0
Federal Home Loan Bank stock	25,673	25,673
Federal Reserve Bank stock	4,886	4,885
Accrued interest receivable	13,545	12,790
Mortgage servicing rights	0	0
Financial liabilities: [Abstract]
Deposits	2,313,712	2,297,632
Repurchase agreements	0	0
Federal funds purchased	15,272	12,314
Advances from Federal Home Loan Bank	1,668	1,719
Long-term debt	0	0
Accrued interest payable	1,477	1,309
Unrecognized financial instruments: [Abstract]
Letters of credit	0	0
Commitments to extend credit	0	0
Forward sale commitments	0	0
Significant Unobservable Inputs (Level 3) [Member]
Financial assets: [Abstract]
Cash and cash equivalents	0	0
Certificates of deposits in other banks	0	0
Securities available-for-sale	0	0
Securities held-to-maturity	0	0
Loans held for sale	0	0
Loans, net	2,542,905	2,540,272
Federal Home Loan Bank stock	0	0
Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	2,652	2,364
Financial liabilities: [Abstract]
Deposits	0	0
Repurchase agreements	213,556	210,008
Federal funds purchased	0	0
Advances from Federal Home Loan Bank	0	0
Long-term debt	31,227	31,185
Accrued interest payable	0	0
Unrecognized financial instruments: [Abstract]
Letters of credit	0	0
Commitments to extend credit	0	0
Forward sale commitments	0	0
Carrying Amount [Member]
Financial assets: [Abstract]
Cash and cash equivalents	167,944	207,560
Certificates of deposits in other banks	9,320	5,336
Securities available-for-sale	677,510	603,343
Securities held-to-maturity	1,662	1,662
Loans held for sale	1,449	22,486
Loans, net	2,529,921	2,517,328
Federal Home Loan Bank stock	25,673	25,673
Federal Reserve Bank stock	4,886	4,885
Accrued interest receivable	13,545	12,970
Mortgage servicing rights	2,652	2,364
Financial liabilities: [Abstract]
Deposits	2,933,580	2,903,848
Repurchase agreements	213,573	210,120
Federal funds purchased	15,272	12,314
Advances from Federal Home Loan Bank	1,387	1,429
Long-term debt	61,341	61,341
Accrued interest payable	1,477	1,309
Unrecognized financial instruments: [Abstract]
Letters of credit	0	0
Commitments to extend credit	0	0
Forward sale commitments	$ 0	$ 0