Note 3 - Investment Securities (Details Textual) - USD ($)	1 Months Ended	3 Months Ended
	Sep. 30, 2018	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Assets [Abstract]
Interest Receivable		$ 4,442,000		$ 4,788,000
Debt Securities, Available-for-Sale and Held-to-Maturity, Allowance for Credit Loss		$ 0
Available-for-Sale, Securities in Unrealized Loss Positions, Depreciation from Amortized Cost Percentage		7.80%
Held-to-maturity, Securities in Unrealized Loss Positions, Depreciation from Amortized Cost Percentage		37.10%
Debt Securities, Available-for-Sale, Realized Gain		$ 133,000
Debt Securities, Available-for-Sale, Realized Loss		101,000
Proceeds from Sale of Debt Securities, Available-for-Sale		19,189,000	$ 0
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss		$ 2,000,000		$ 2,400,000
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]		Interest Receivable		Interest Receivable
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss		$ 18,000		$ 18,000
Investment, Number of Shares Acquired (in shares)	90,000
Investment Ownership Percentage	5.00%
Payments to Acquire Other Investments	$ 1,900,000
Equity Securities, FV-NI, Unrealized Gain (Loss)		(68,000)	137,000
Equity Securities, FV-NI, Current		1,200,000		1,300,000
Investment Company, Financial Support to Investee Contractually Required, Not Provided, Amount		530,000
Limited Partnership Interest, Technology Fund [Member]
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount		0	$ 0
Limited Partnership Interest, Technology Fund [Member] | Other Assets [Member]
Equity Securities without Readily Determinable Fair Value, Amount		$ 1,000,000		$ 1,000,000