Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Investments in Affordable Housing and Alternative Energy Partnerships	$ 315,700	$ 327,100
Number of Limited Partnerships Deemed to be Variable Interest Entities	11
Increase in Total Assets and Liabilities from Consolidating Affordable Housing Equity Interest	$ 25,300	31,300
Alternative Energy Tax Credit Partnership Investments, Net	19,943	37,208
Alternative Energy Tax Credit Partnership Investments, Held in Escrow	6,400	25,400
Asset Impairment Charges	4,296	4,145	$ 1,172
Affordable Housing Limited Partnerships [Member]
Asset Impairment Charges	7,700	$ 6,200
Domestic Tax Authority [Member]
Remaining and Future Available Tax Credit	249,600
State and Local Jurisdiction [Member]
Remaining and Future Available Tax Credit	$ 6,200