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 ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Borrowing Availability Through Credit Lines and Federal Funds Purchased Agreements						$ 264,600,000
Long-Term Debt						637,000	$ 658,000
Subordinated Debt						$ 103,782,000	103,296,000
Number of Statutory Business Trusts						3
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust						$ 19,589,000	19,589,000
Proceeds from Issuance of Common Stock						$ 244,000	203,000	$ 294,000
Trust Preferred Securities Limited to Tier One Capital Elements Net of Goodwill						25.00%
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
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]
Investment Owned, Net Assets, 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						$ 74,000,000	73,700,000
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						29,800,000	$ 29,600,000
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%
Subsidiaries [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available						1,300,000,000
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						258,600,000
Line of Credit [Member] | Federal Reserve Bank Advances [Member] | Financing Receivables Utilized to Secure Line of Credit [Member]
Debt Instrument, Collateral Amount						$ 520,600,000
Federal Home Loan Bank Advances [Member]
Long-Term Debt, Weighted Average Interest Rate, at Point in Time						5.34%	5.34%
Federal Home Loan Bank Advances [Member] | Blanket Lien [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged						$ 2,300,000,000