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, 2021	Dec. 31, 2020
Financial assets [Abstract]
Debt securities available-for-sale	$ 1,155,195	$ 997,261
Equity securities at fair value	2,243	2,471
Federal Reserve Bank stock	4,887	4,887
Mortgage servicing rights	5,584	4,068
Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	423,105	338,235
Certificates of deposits in other banks	245	245
Debt securities available-for-sale	1,155,195	997,261
Equity securities at fair value	2,243	2,471
Loans held for sale	17,748	23,259
Loans, net	3,493,458	3,506,189
Federal Home Loan Bank stock	9,971	10,048
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	15,188	15,818
Mortgage servicing rights	5,584	4,068
Financial liabilities [Abstract]
Deposits	4,233,772	4,016,082
Repurchase agreements	354,235	355,862
Federal funds purchased	500	500
Advances from Federal Home Loan Bank	390	395
Long-term debt	57,841	57,841
Accrued interest payable	1,365	1,243
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	423,105	338,235
Certificates of deposits in other banks	0	0
Debt securities available-for-sale	134,598	74,991
Equity securities at fair value	0	0
Loans held for sale	18,195	23,884
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	1,283,309	1,140,925
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	245	245
Debt securities available-for-sale	1,020,597	922,270
Equity securities at fair value	0	0
Loans held for sale	0	0
Loans, net	0	0
Federal Home Loan Bank stock	9,971	10,048
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	15,188	15,818
Mortgage servicing rights	0	0
Financial liabilities [Abstract]
Deposits	3,002,615	2,913,217
Repurchase agreements	0	0
Federal funds purchased	500	500
Advances from Federal Home Loan Bank	427	436
Long-term debt	0	0
Accrued interest payable	1,365	1,243
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
Debt securities available-for-sale	0	0
Equity securities at fair value	2,243	2,471
Loans held for sale	0	0
Loans, net	3,649,893	3,658,554
Federal Home Loan Bank stock	0	0
Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	5,584	4,068
Financial liabilities [Abstract]
Deposits	0	0
Repurchase agreements	354,158	355,918
Federal funds purchased	0	0
Advances from Federal Home Loan Bank	0	0
Long-term debt	38,425	40,081
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