Note 4 - Investment Securities Available for Sale - Amortized Cost and Estimated Fair Value of Investment Securities (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Investment securities available for sale, amortized cost	$ 535,269,000	$ 498,886,000
Investment securities available for sale, gross unrealized gains	1,883,000	600,000
Investment securities available for sale, gross unrealized losses	(47,971,000)	(54,783,000)
Estimated fair value	489,181,000	444,703,000
US Treasury Securities [Member]
Investment securities available for sale, amortized cost	6,978,000	9,950,000
Investment securities available for sale, gross unrealized gains	0	0
Investment securities available for sale, gross unrealized losses	(98,000)	(243,000)
Estimated fair value	6,880,000	9,707,000
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, amortized cost	256,694,000	238,253,000
Investment securities available for sale, gross unrealized gains	351,000	214,000
Investment securities available for sale, gross unrealized losses	(21,114,000)	(24,059,000)
Estimated fair value	235,931,000	214,408,000
Commercial Mortgage Backed Securities Issued by US Government Agencies [Member]
Investment securities available for sale, amortized cost	129,321,000	112,142,000
Investment securities available for sale, gross unrealized gains	465,000	143,000
Investment securities available for sale, gross unrealized losses	(13,834,000)	(12,704,000)
Estimated fair value	115,952,000	99,581,000
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, amortized cost	142,276,000	138,541,000
Investment securities available for sale, gross unrealized gains	1,067,000	243,000
Investment securities available for sale, gross unrealized losses	(12,925,000)	(17,777,000)
Estimated fair value	$ 130,418,000	$ 121,007,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
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-Section S99
-Paragraph 1
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