Note 4 - Loans and the Allowance for Credit Losses - Loan Modifications (Details) - Extended Maturity [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Dec. 31, 2023
% of total segment financing receivables		0.62%
Modified		$ 5,856
Commercial Portfolio Segment [Member] \| Commercial Loans [Member]
Modified	$ 36	$ 1,489
% of total segment financing receivables	0.04%	1.92%
Commercial Portfolio Segment [Member] \| Agricultural Loans [Member]
Modified		$ 4,367
% of total segment financing receivables		3.32%

Amortized cost of financing receivable modified during period for debtor experiencing financial difficulty.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 2: 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

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration