Note 7 - Stock Compensation Plans (Details Textual) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024	May 10, 2023
Share-Based Payment Arrangement, Expense	$ 0	$ 0
Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Expense	$ 265	142
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	18,455
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 1,100	$ 464
Restricted Stock Units (RSUs) [Member] \| Vesting on February 15, 2025 [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	3,851
Restricted Stock Units (RSUs) [Member] \| Three Year Vesting [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	14,604
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)	3 years
First National Corporation 2023 Stock Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)			325,000

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479983/718-10-S45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
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-Section S99
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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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