Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Investments in Affordable Housing and Alternative Energy Partnerships		$ 327,100	$ 299,200
Number of Limited Partnerships Deemed to be Variable Interest Entities			10
Increase in Total Assets and Liabilities from Consolidating Affordable Housing Equity Interest		31,300	$ 31,100
Alternative Energy Tax Credit Partnership Investments, Net	$ 37,208	37,200	11,694
Alternative Energy Tax Credit Partnership Investments, Held in Escrow		25,400	690,000
Asset Impairment Charges, Total	$ 4,145		1,172	$ 7,836
Affordable Housing Limited Partnerships [Member]
Asset Impairment Charges, Total		6,200	$ 1,800
Affordable Housing Limited Partnerships [Member] | Domestic Tax Authority [Member]
Remaining and Future Available Tax Credit		238,600
Affordable Housing Limited Partnerships [Member] | State and Local Jurisdiction [Member]
Remaining and Future Available Tax Credit		$ 7,900