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	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financial assets [Abstract]
Debt securities available-for-sale	$ 997,261	$ 599,844
Debt securities held-to-maturity	0	517
Equity securities at fair value	2,471	1,953
Federal Reserve Bank stock	4,887	4,887
Mortgage servicing rights	4,068	3,263	$ 3,607	$ 3,484
Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	338,235	264,683
Certificates of deposit in other banks	245	245
Debt securities available-for-sale	997,261	599,844
Debt securities held-to-maturity		517
Equity securities at fair value	2,471	1,953
Loans held for sale	23,259	1,167
Loans, net	3,506,189	3,213,568
Federal Home Loan Bank stock	10,048	10,474
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	15,818	14,836
Mortgage servicing rights	4,068	3,263
Financial liabilities [Abstract]
Deposits	4,016,082	3,405,572
Repurchase agreements	355,862	226,917
Federal funds purchased	500	7,906
Advances from Federal Home Loan Bank	395	415
Long-term debt	57,841	57,841
Accrued interest payable	1,243	2,839
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	338,235	264,683
Certificates of deposit in other banks	0	0
Debt securities available-for-sale	74,991	54,263
Debt securities held-to-maturity		0
Equity securities at fair value	0	0
Loans held for sale	23,884	1,191
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	1,140,925	865,760
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 deposit in other banks	245	245
Debt securities available-for-sale	922,270	545,581
Debt securities held-to-maturity		517
Equity securities at fair value	0	0
Loans held for sale	0	0
Loans, net	0	0
Federal Home Loan Bank stock	10,048	10,474
Federal Reserve Bank stock	4,887	4,887
Accrued interest receivable	15,818	14,836
Mortgage servicing rights	0	0
Financial liabilities [Abstract]
Deposits	2,913,217	2,560,271
Repurchase agreements	0	0
Federal funds purchased	500	7,906
Advances from Federal Home Loan Bank	436	446
Long-term debt	0	0
Accrued interest payable	1,243	2,839
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 deposit in other banks	0	0
Debt securities available-for-sale	0	0
Debt securities held-to-maturity		0
Equity securities at fair value	2,471	1,953
Loans held for sale	0	0
Loans, net	3,658,554	3,283,876
Federal Home Loan Bank stock	0	0
Federal Reserve Bank stock	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	4,068	3,263
Financial liabilities [Abstract]
Deposits	0	0
Repurchase agreements	355,918	226,921
Federal funds purchased	0	0
Advances from Federal Home Loan Bank	0	0
Long-term debt	40,081	49,382
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