Note 2 - Investment Securities (Details Textual)	3 Months Ended	9 Months Ended
	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Mar. 07, 2022 USD ($)
Debt Securities, Held-to-Maturity, Number of Securities		0
Debt Securities, Held-to-Maturity, Allowance for Credit Loss, Ending Balance		$ 0
Debt Securities, Held-to-Maturity, Nonaccrual		0		$ 0
Debt Securities, Available-for-sale, Number of Positions Sold	3
Proceeds from Sale of Debt Securities, Available-for-Sale	$ 2,000,000	0	$ 2,111,000
Debt Securities, Available-for-Sale, Gain (Loss), Total	$ (92,000)
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Ending Balance		$ 0
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions		543		547
Debt Securities, Available-for-Sale, Unrealized Loss Position, Percentage		99.00%		98.00%
Collateral Pledged [Member]
Debt Securities, Available-for-Sale, Restricted		$ 688,000,000		$ 1,100,000,000
Commonwealth [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities					$ 247,000,000
Other Assets [Member]
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss		4,000,000		4,000,000
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss		$ 1,000,000		$ 2,000,000