Note 4 - Loans and the Allowance for Credit Losses - Financial Effect of Loan Modifications (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2024	Dec. 31, 2023
Weighted average term extension (Month)		9 months 3 days
Commercial Portfolio Segment [Member] \| Commercial Loans [Member]
Weighted average term extension (Month)	6 months	6 months
Commercial Portfolio Segment [Member] \| Agricultural Loans [Member]
Weighted average term extension (Month)		10 months

Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration