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Note 17 - Lease Commitments (Details Textual) $ in Thousands | Dec. 31, 2020 | Jan. 01, 2019 USD ($)
--- | --- | ---
Number of Leases | 6 |
Leases With Option to Extend the Lease [Member] |  |
Number of Leases | 4 |
Accounting Standards Update 2016-02 [Member] |  |
Operating Lease, Right-of-Use Asset |  | $ 390

X
- Definition Represents the number of leases. + References No definition available. + Details
Name: | fxnc_NumberOfLeases
Namespace Prefix: | fxnc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of lessee's right to use underlying asset under operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977 + Details
Name: | us-gaap_OperatingLeaseRightOfUseAsset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_LeaseContractualTermAxis=fxnc_LeasesWithOptionToExtendTheLeaseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |