<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.4.0.6</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>214</ContextCount>
  <ElementCount>313</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>48</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>0110 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/BalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>0111 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/BalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>0120 - Statement - Consolidated Statements of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/StatementsOfIncome</Role>
      <ShortName>Consolidated Statements of Income (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>0121 - Statement - Consolidated Statements of Income (Parenthetical) (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/StatementsOfIncomeParenthetical</Role>
      <ShortName>Consolidated Statements of Income (Parenthetical) (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>0130 - Statement - Consolidated Statements of Comprehensive Income (Loss) (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/StatementsOfComprehensiveIncomeLoss</Role>
      <ShortName>Consolidated Statements of Comprehensive Income (Loss) (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>0131 - Statement - Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/StatementsOfComprehensiveIncomeLossParenthetical</Role>
      <ShortName>Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>0140 - Statement - Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/StatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>0150 - Statement - Consolidated Statements of Changes in Shareholders' Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/StatementsOfChangesInShareholdersEquity</Role>
      <ShortName>Consolidated Statements of Changes in Shareholders' Equity (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>0201 - Disclosure - General</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/General</Role>
      <ShortName>General</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>0202 - Disclosure - Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/Securities</Role>
      <ShortName>Securities</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>0203 - Disclosure - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/Loans</Role>
      <ShortName>Loans</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>0204 - Disclosure - Allowance for Loan Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AllowanceForLoanLosses</Role>
      <ShortName>Allowance for Loan Losses</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>0205 - Disclosure - Other Real Estate Owned (OREO)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherRealEstateOwned</Role>
      <ShortName>Other Real Estate Owned (OREO)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>0206 - Disclosure - Other Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherBorrowings</Role>
      <ShortName>Other Borrowings</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>0207 - Disclosure - Capital Requirements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/CapitalRequirements</Role>
      <ShortName>Capital Requirements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>0208 - Disclosure - Trust Preferred Capital Notes</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://fbvirginia.com/role/TrustPreferredCapitalNotes</Role>
      <ShortName>Trust Preferred Capital Notes</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>0209 - Disclosure - Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/BenefitPlans</Role>
      <ShortName>Benefit Plans</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>0210 - Disclosure - Earnings per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/EarningsPerCommonShare</Role>
      <ShortName>Earnings per Common Share</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>0211 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>0212 - Disclosure - Capital Purchase Program</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/CapitalPurchaseProgram</Role>
      <ShortName>Capital Purchase Program</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>0213 - Disclosure - Accumulated Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AccumulatedOtherComprehensiveIncome</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>0401 - Disclosure - General (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/GeneralPolicies</Role>
      <ShortName>General (Policies)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>0502 - Disclosure - Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/SecuritiesTables</Role>
      <ShortName>Securities (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>0503 - Disclosure - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/LoansTables</Role>
      <ShortName>Loans (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>0504 - Disclosure - Allowance for Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AllowanceForLoanLossesTables</Role>
      <ShortName>Allowance for Loan Losses (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>0505 - Disclosure - Other Real Estate Owned (OREO) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherRealEstateOwnedTables</Role>
      <ShortName>Other Real Estate Owned (OREO) (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>0507 - Disclosure - Capital Requirements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/CapitalRequirementsTables</Role>
      <ShortName>Capital Requirements (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>0509 - Disclosure - Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/BenefitPlansTables</Role>
      <ShortName>Benefit Plans (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>0511 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>0513 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AccumulatedOtherComprehensiveIncomeTables</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>0602 - Disclosure - Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/SecuritiesDetails</Role>
      <ShortName>Securities (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>06021 - Disclosure - Securities (Details 1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/SecuritiesDetails1</Role>
      <ShortName>Securities (Details 1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>06022 - Disclosure - Securities (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/SecuritiesDetail2</Role>
      <ShortName>Securities (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>06023 - Disclosure - Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/SecuritiesDetailsTextual</Role>
      <ShortName>Securities (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>0603 - Disclosure - Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/LoansDetails</Role>
      <ShortName>Loans (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>06031 - Disclosure - Loans (Details 1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/LoansDetails1</Role>
      <ShortName>Loans (Details 1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>06032 - Disclosure - Loans (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/LoansDetails2</Role>
      <ShortName>Loans (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>06033 - Disclosure - Loans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/LoansDetailsTextual</Role>
      <ShortName>Loans (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>0604 - Disclosure - Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AllowanceForLoanLossesDetails</Role>
      <ShortName>Allowance for Loan Losses (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>06041 - Disclosure - Allowance for Loan Losses (Details 1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AllowanceForLoanLossesDetails1</Role>
      <ShortName>Allowance for Loan Losses (Details 1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>06042 - Disclosure - Allowance for Loan Losses (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AllowanceForLoanLossesDetails2</Role>
      <ShortName>Allowance for Loan Losses (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>06043 - Disclosure - Allowance for Loan Losses (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AllowanceForLoanLossesDetailsTextual</Role>
      <ShortName>Allowance for Loan Losses (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>0605 - Disclosure - Other Real Estate Owned (OREO) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherRealEstateOwnedDetails</Role>
      <ShortName>Other Real Estate Owned (OREO) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>06051 - Disclosure - Other Real Estate Owned (OREO) (Details 1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherRealEstateOwnedDetails1</Role>
      <ShortName>Other Real Estate Owned (OREO) (Details 1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>06052 - Disclosure - Other Real Estate Owned (OREO) (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherRealEstateOwnedDetailsTextual</Role>
      <ShortName>Other Real Estate Owned (OREO) (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>0606 - Disclosure - Other Borrowings (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/OtherBorrowingsDetailsTextual</Role>
      <ShortName>Other Borrowings (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>0607 - Disclosure - Capital Requirements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/CapitalRequirementsDetails</Role>
      <ShortName>Capital Requirements (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>06071 - Disclosure - Capital Requirements (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/CapitalRequirementsDetailsTextual</Role>
      <ShortName>Capital Requirements (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>0608 - Disclosure - Trust Preferred Capital Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://fbvirginia.com/role/TrustPreferredCapitalNotesDetailsTextual</Role>
      <ShortName>Trust Preferred Capital Notes (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>0609 - Disclosure - Benefit Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/BenefitPlansDetails</Role>
      <ShortName>Benefit Plans (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>06091 - Disclosure - Benefit Plans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/BenefitPlansDetailsTextual</Role>
      <ShortName>Benefit Plans (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>0610 - Disclosure - Earnings per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/EarningsPerCommonShareDetails</Role>
      <ShortName>Earnings per Common Share (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>0611 - Disclosure - Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurements (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>06111 - Disclosure - Fair Value Measurements (Details 1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurementsDetails1</Role>
      <ShortName>Fair Value Measurements (Details 1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>06112 - Disclosure - Fair Value Measurements (Details 2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurementsDetails2</Role>
      <ShortName>Fair Value Measurements (Details 2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>06113 - Disclosure - Fair Value Measurements (Details 3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurementsDetails3</Role>
      <ShortName>Fair Value Measurements (Details 3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>06114 - Disclosure - Fair Value Measurements (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/FairValueMeasurementsDetails4</Role>
      <ShortName>Fair Value Measurements (Details Textual)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>0612 - Disclosure - Capital Purchase Program (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/CapitalPurchaseProgramDetails</Role>
      <ShortName>Capital Purchase Program (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>0613 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fbvirginia.com/role/AccumulatedOtherComprehensiveIncomeDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">Element us-gaap_NotesPayable had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">'Monetary' elements on report '06043 - Disclosure - Allowance for Loan Losses (Details Textual)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '0606 - Disclosure - Other Borrowings (Details Textual)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 0110 - Statement - Consolidated Balance Sheets</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 0111 - Statement - Consolidated Balance Sheets (Parenthetical)</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 0120 - Statement - Consolidated Statements of Income (Unaudited)</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2012'</Log>
    <Log type="Info">Process Flow-Through: 0121 - Statement - Consolidated Statements of Income (Parenthetical) (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 0130 - Statement - Consolidated Statements of Comprehensive Income (Loss) (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 0131 - Statement - Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 0140 - Statement - Consolidated Statements of Cash Flows (Unaudited)</Log>
  </Logs>
  <InputFiles>
    <File>fxnc-20130331.xml</File>
    <File>fxnc-20130331.xsd</File>
    <File>fxnc-20130331_cal.xml</File>
    <File>fxnc-20130331_def.xml</File>
    <File>fxnc-20130331_lab.xml</File>
    <File>fxnc-20130331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
