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Allowance for Loan Losses - Allowance by Impairment Methodology and Loans by Impairment Methodology (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Allowance for loan losses: |  |  |
Balance at beginning of year | $ 10,644 us-gaap_LoansAndLeasesReceivableAllowance | $ 13,075 us-gaap_LoansAndLeasesReceivableAllowance | $ 12,937 us-gaap_LoansAndLeasesReceivableAllowance
Charge-offs | (927)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs | (4,492)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs | (3,793)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Recoveries | 851 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts | 2,486 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts | 376 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Provision for (recovery of) loan losses | (3,850)us-gaap_ProvisionForLoanAndLeaseLosses | (425)us-gaap_ProvisionForLoanAndLeaseLosses | 3,555 us-gaap_ProvisionForLoanAndLeaseLosses
Balance at end of year | 6,718 us-gaap_LoansAndLeasesReceivableAllowance | 10,644 us-gaap_LoansAndLeasesReceivableAllowance | 13,075 us-gaap_LoansAndLeasesReceivableAllowance
Ending Balance: |  |  |
Allowance for loan losses, Individually evaluated for impairment | 1,907 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 | 1,379 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 | 1,838 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Allowance for loan losses, Collectively evaluated for impairment | 4,811 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment | 9,265 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment | 11,237 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Loans: |  |  |
Ending Balance | 378,410 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount | 357,093 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount | 383,594 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Loans, Individually evaluated for impairment | 13,922 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | 21,694 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | 16,980 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Loans, Collectively evaluated for impairment | 364,488 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment | 335,399 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment | 366,614 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Construction and Land Development [Member] |  |  |
Allowance for loan losses: |  |  |
Balance at beginning of year | 2,710 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 2,481 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 2,843 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Charge-offs | (91)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | (2,962)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | (431)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Recoveries | 80 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember |  | 1 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Provision for (recovery of) loan losses | (1,296)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 3,191 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 68 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Balance at end of year | 1,403 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 2,710 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 2,481 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Ending Balance: |  |  |
Allowance for loan losses, Individually evaluated for impairment | 245 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 882 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 567 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Allowance for loan losses, Collectively evaluated for impairment | 1,158 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 1,828 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 1,914 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Loans: |  |  |
Ending Balance | 29,475 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 34,060 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 43,524 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Loans, Individually evaluated for impairment | 3,205 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 6,862 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 2,516 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Loans, Collectively evaluated for impairment | 26,270 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 27,198 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember | 41,008 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConstructionAndLandPortfolioSegmentMember
Secured by 1-4 Family Residential [Member] |  |  |
Allowance for loan losses: |  |  |
Balance at beginning of year | 2,975 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 3,712 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 3,766 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Charge-offs | (272)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | (260)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | (761)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Recoveries | 15 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 823 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 68 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Provision for (recovery of) loan losses | (1,514)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | (1,300)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 639 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Balance at end of year | 1,204 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 2,975 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 3,712 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Ending Balance: |  |  |
Allowance for loan losses, Individually evaluated for impairment | 173 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 190 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 306 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Allowance for loan losses, Collectively evaluated for impairment | 1,031 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 2,785 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 3,406 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Loans: |  |  |
Ending Balance | 163,727 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 141,961 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 134,964 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Loans, Individually evaluated for impairment | 3,414 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 3,431 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 3,776 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Loans, Collectively evaluated for impairment | 160,313 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 138,530 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember | 131,188 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ResidentialOneThroughFourFamilyMember
Other Real Estate [Member] |  |  |
Allowance for loan losses: |  |  |
Balance at beginning of year | 4,418 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 6,163 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 5,192 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Charge-offs | (203)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | (1,070)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | (2,154)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Recoveries | 509 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 1,304 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 64 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Provision for (recovery of) loan losses | (1,066)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | (1,979)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 3,061 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Balance at end of year | 3,658 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 4,418 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 6,163 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Ending Balance: |  |  |
Allowance for loan losses, Individually evaluated for impairment | 1,456 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 263 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 930 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Allowance for loan losses, Collectively evaluated for impairment | 2,202 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 4,155 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 5,233 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Loans: |  |  |
Ending Balance | 151,802 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 145,968 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 174,220 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Loans, Individually evaluated for impairment | 7,183 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 11,143 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 10,528 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Loans, Collectively evaluated for impairment | 144,619 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 134,825 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember | 163,692 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_OtherRealEstateMember
Commercial and Industrial [Member] |  |  |
Allowance for loan losses: |  |  |
Balance at beginning of year | 442 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 608 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 963 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Charge-offs | (43)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | (37)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | (261)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Recoveries | 18 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 179 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 35 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Provision for (recovery of) loan losses | (107)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | (308)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | (129)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Balance at end of year | 310 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 442 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 608 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Ending Balance: |  |  |
Allowance for loan losses, Individually evaluated for impairment | 33 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 44 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 35 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Allowance for loan losses, Collectively evaluated for impairment | 277 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 398 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 573 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Loans: |  |  |
Ending Balance | 21,166 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 22,803 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 23,071 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Loans, Individually evaluated for impairment | 120 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 258 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 160 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Loans, Collectively evaluated for impairment | 21,046 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 22,545 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember | 22,911 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_CommercialAndIndustrialLoansMember
Consumer and Other Loans [Member] |  |  |
Allowance for loan losses: |  |  |
Balance at beginning of year | 99 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 111 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 173 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Charge-offs | (318)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | (163)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | (186)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Recoveries | 229 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 180 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 208 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Provision for (recovery of) loan losses | 133 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | (29)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | (84)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Balance at end of year | 143 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 99 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 111 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Ending Balance: |  |  |
Allowance for loan losses, Collectively evaluated for impairment | 143 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 99 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 111 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Loans: |  |  |
Ending Balance | 12,240 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 12,301 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | 7,815 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember
Loans, Collectively evaluated for impairment | $ 12,240 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | $ 12,301 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember | $ 7,815 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fxnc_ConsumerAndOtherLoansMember

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- Definition Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph d -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
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- Definition Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522 + Details
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