Note 13 - Borrowed Funds (Details Textual)	1 Months Ended			3 Months Ended		12 Months Ended
	Dec. 31, 2005 USD ($)	Mar. 31, 2004 USD ($)	Oct. 31, 2002 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Federal Home Loan Bank Collateral Amount for Advances						$ 1,800,000,000
Federal Reserve Bank, Amount of Loans Pledged For Line of Credit						506,000,000.0
Borrowing Availability Through Credit Lines and Federal Funds Purchased Agreements						290,400,000
Federal Funds Purchased				$ 146,000		149,000	$ 146,000
Long-Term Debt, Total				679,000		658,000	679,000
Subordinated Debt, Ending Balance				102,891,000		$ 103,296,000	102,891,000
Number of Statutory Business Trusts						3
Proceeds from Issuance of Common Stock						$ 203,000	294,000	$ 178,000
Trust Preferred Securities Limited to Tier One Capital Elements Net of Goodwill						25.00%
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total				19,589,000		$ 19,589,000	19,589,000
SFG Capital Trust I [Member]
Debt Instrument, Basis Spread on Variable Rate			3.45%
Proceeds from Issuance or Sale of Equity, Total			$ 3,500,000
Proceeds from Issuance of Common Stock			109,000
Payments to Acquire Investments, Total			$ 3,610,000
SFG Capital Trust II [Member]
Debt Instrument, Basis Spread on Variable Rate		2.80%
Proceeds from Issuance or Sale of Equity, Total		$ 7,500,000
Proceeds from Issuance of Common Stock		232,000
Payments to Acquire Investments, Total		$ 7,730,000
SFG Capital Trust III [Member]
Debt Instrument, Basis Spread on Variable Rate	1.45%
Proceeds from Issuance or Sale of Equity, Total	$ 8,000,000.0
Proceeds from Issuance of Common Stock	248,000
Payments to Acquire Investments, Total	$ 8,250,000
SFG Capital Trust I, SFG Capital Trust II and SFG Capital Trust III [Member]
Equity Method Investment, Ownership Percentage						100.00%
Issued Fourth Quarter2021 [Member]
Debt Instrument, Face Amount				75,000,000			75,000,000
Debt Issuance Costs, Net, Total				1,740,000			1,740,000
Subordinated Debt, Ending Balance				$ 73,400,000		$ 73,700,000	73,400,000
Number of Maturity Years Remaining to Qualify as Tier2 Capital (Year)				5 years
Percent Reduction Each Year to Tier 2 Capital Until Subordinated Debt Maturity Date				20.00%
Subordinated Borrowing, Interest Rate				3.25%
Debt Instrument, Term (Year)				10 years
Number of Years Subordinated Debt Not Pre Payable (Year)				5 years
Issued Fourth Quarter2021 [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Debt Instrument, Basis Spread on Variable Rate				2.30%
Issued Third Quarter 2020 [Member]
Debt Instrument, Face Amount					$ 30,000,000
Debt Issuance Costs, Net, Total					$ 681,000
Subordinated Debt, Ending Balance				$ 29,500,000		$ 29,600,000	$ 29,500,000
Number of Maturity Years Remaining to Qualify as Tier2 Capital (Year)					5 years
Percent Reduction Each Year to Tier 2 Capital Until Subordinated Debt Maturity Date					20.00%
Subordinated Borrowing, Interest Rate					5.00%
Debt Instrument, Term (Year)					10 years
Number of Years Subordinated Debt Not Pre Payable (Year)					5 years
Issued Third Quarter 2020 [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Debt Instrument, Basis Spread on Variable Rate					4.87%
Federal Home Loan Bank Advances [Member]
Long-Term Debt, Weighted Average Interest Rate, at Point in Time				5.34%		5.34%	5.34%
Subsidiaries [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available						$ 1,040,000,000.00
Line of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity						6,000,000
Line of Credit [Member] | Federal Reserve Bank Advances [Member]
Line of Credit Facility, Maximum Borrowing Capacity						$ 284,400,000