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	Mar. 31, 2019	Dec. 31, 2018
Financial assets [Abstract]
Securities available-for-sale	$ 599,299	$ 593,746
Securities held-to-maturity	619	649
Equity securities at fair value	1,528	1,173
Mortgage servicing rights	3,390	3,607
Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	253,860	141,450
Certificates of deposits in other banks	1,470	3,920
Securities available-for-sale	599,299	593,746
Securities held-to-maturity	619	649
Equity securities at fair value	1,528	1,173
Loans held for sale	13,649	2,461
Loans, net	3,154,728	3,172,730
Federal Home Loan Bank stock	12,261	14,713
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	15,188	14,432
Mortgage servicing rights	3,390	3,607
Financial liabilities [Abstract]
Deposits	3,383,103	3,305,950
Repurchase agreements	237,506	232,712
Federal funds purchased	1,800	1,180
Advances from Federal Home Loan Bank	431	436
Long-term debt	59,341	59,341
Accrued interest payable	3,983	2,902
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	253,860	141,450
Certificates of deposits in other banks	0	0
Securities available-for-sale	56,744	91,028
Securities held-to-maturity	0	0
Equity securities at fair value	0	0
Loans held for sale	13,752	2,518
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	841,996	803,316
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	1,470	3,914
Securities available-for-sale	542,555	502,718
Securities held-to-maturity	619	649
Equity securities at fair value	0	0
Loans held for sale	0	0
Loans, net	0	0
Federal Home Loan Bank stock	12,261	14,713
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	15,188	14,432
Mortgage servicing rights	0	0
Financial liabilities [Abstract]
Deposits	2,559,903	2,513,084
Repurchase agreements	0	0
Federal funds purchased	1,800	1,180
Advances from Federal Home Loan Bank	461	468
Long-term debt	0	0
Accrued interest payable	3,983	2,902
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
Securities available-for-sale	0	0
Securities held-to-maturity	0	0
Equity securities at fair value	1,528	1,173
Loans held for sale	0	0
Loans, net	3,150,772	3,175,908
Federal Home Loan Bank stock	0	0
Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	3,390	3,607
Financial liabilities [Abstract]
Deposits	0	0
Repurchase agreements	237,556	232,796
Federal funds purchased	0	0
Advances from Federal Home Loan Bank	0	0
Long-term debt	44,166	44,166
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