Fair Market Value of Financial Assets and Liabilities, Estimated Fair Value of Financial Instruments and Indication of Level Within Fair Value Hierarchy of Valuation Techniques (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial assets [Abstract]
Available-for-sale securities	$ 603,033	$ 605,394
Securities held-to-maturity	858	867
Mortgage servicing rights	3,283	3,433
Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	166,416	144,716
Certificates of deposits in other banks	11,270	980
Available-for-sale securities	603,033	605,394
Securities held-to-maturity	858	866
Loans held for sale	1,605	1,244
Loans, net	3,077,030	2,902,438
Federal Home Loan Bank stock	17,927	17,927
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	12,920	11,922
Mortgage servicing rights	3,283	3,433
Financial liabilities [Abstract]
Deposits	3,200,366	3,081,308
Repurchase agreements	260,007	251,065
Federal funds purchased	8,196	4,816
Advances from Federal Home Loan Bank	50,869	944
Long-term debt	59,341	61,341
Accrued interest payable	2,771	1,200
Unrecognized financial instruments [Abstract]
Letters of credit	0	0
Commitments to extend credit	0	0
Forward sale commitments	0	0
Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets [Abstract]
Cash and cash equivalents	166,416	144,716
Certificates of deposits in other banks	0	0
Available-for-sale securities	89,613	69,292
Securities held-to-maturity	0	0
Loans held for sale	1,651	1,260
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	786,856	767,918
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
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Certificates of deposits in other banks	11,244	982
Available-for-sale securities	513,420	536,102
Securities held-to-maturity	858	867
Loans held for sale	0	0
Loans, net	0	0
Federal Home Loan Bank stock	17,927	17,927
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	12,920	11,922
Mortgage servicing rights	0	0
Financial liabilities [Abstract]
Deposits	2,410,741	2,321,690
Repurchase agreements	0	0
Federal funds purchased	8,196	4,816
Advances from Federal Home Loan Bank	50,870	1,009
Long-term debt	0	0
Accrued interest payable	2,771	1,200
Unrecognized financial instruments [Abstract]
Letters of credit	0	0
Commitments to extend credit	0	0
Forward sale commitments	0	0
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Certificates of deposits in other banks	0	0
Available-for-sale securities	0	0
Securities held-to-maturity	0	0
Loans held for sale	0	0
Loans, net	3,057,809	2,882,348
Federal Home Loan Bank stock	0	0
Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	3,283	3,433
Financial liabilities [Abstract]
Deposits	0	0
Repurchase agreements	260,044	250,820
Federal funds purchased	0	0
Advances from Federal Home Loan Bank	0	0
Long-term debt	49,073	49,073
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