Note 5 - Investments in Affordable Housing and Alternative Energy Partnerships (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Investments in Affordable Housing and Alternative Energy Partnerships	$ 299,200	$ 309,000
Number of Limited Partnerships Deemed to be Variable Interest Entities	10
Increase in Total Assets and Liabilities from Consolidating Affordable Housing Equity Interest	$ 31,100	31,400
Alternative Energy Tax Credit Partnership Investments, Net	11,694	29,035
Alternative Energy Tax Credit Partnership Investments, Held in Escrow	690,000
Asset Impairment Charges, Total	1,172	7,836	$ 848
Affordable Housing Limited Partnerships [Member]
Asset Impairment Charges, Total	1,800	$ 1,400
Affordable Housing Limited Partnerships [Member] | Domestic Tax Authority [Member]
Remaining and Future Available Tax Credit	231,800
Affordable Housing Limited Partnerships [Member] | State and Local Jurisdiction [Member]
Remaining and Future Available Tax Credit	$ 4,500