<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.7.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>778</ContextCount>
  <ElementCount>369</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>112</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Condensed Consolidated Balance Sheets (Current Period Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Current Period Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited-parentheticals</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Condensed Consolidated Statements of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-statements-of-income-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Condensed Consolidated Statements of Comprehensive Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-statements-of-comprehensive-income-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-statements-of-changes-in-stockholders-equity-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Statement - Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-statements-of-changes-in-stockholders-equity-unaudited-parentheticals</Role>
      <ShortName>Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-condensed-consolidated-statements-of-cash-flows-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Disclosure - Note 1 - Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-1-basis-of-presentation</Role>
      <ShortName>Note 1 - Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 2 - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities</Role>
      <ShortName>Note 2 - Investment Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 3 - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans</Role>
      <ShortName>Note 3 - Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 4 - Credit Quality</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality</Role>
      <ShortName>Note 4 - Credit Quality</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 5 - Allowance for Loan Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-5-allowance-for-loan-losses</Role>
      <ShortName>Note 5 - Allowance for Loan Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 6 - FDIC Indemnification Asset</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-6-fdic-indemnification-asset</Role>
      <ShortName>Note 6 - FDIC Indemnification Asset</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 7 - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-7-deposits</Role>
      <ShortName>Note 7 - Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 8 - Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-8-borrowings</Role>
      <ShortName>Note 8 - Borrowings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 9 - Derivative Instruments and Hedging Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-9-derivative-instruments-and-hedging-activities</Role>
      <ShortName>Note 9 - Derivative Instruments and Hedging Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 10 - Employee Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-10-employee-benefit-plans</Role>
      <ShortName>Note 10 - Employee Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 11 - Accumulated Other Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-11-accumulated-other-comprehensive-income</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 12 - Fair Value</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-12-fair-value</Role>
      <ShortName>Note 12 - Fair Value</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 13 - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-13-earnings-per-share</Role>
      <ShortName>Note 13 - Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Document - Note 14 - Litigation, Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-14-litigation-commitments-and-contingencies</Role>
      <ShortName>Note 14 - Litigation, Commitments and Contingencies</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 2 - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-tables</Role>
      <ShortName>Note 2 - Investment Securities (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Note 3 - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans-tables</Role>
      <ShortName>Note 3 - Loans (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Note 4 - Credit Quality (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-tables</Role>
      <ShortName>Note 4 - Credit Quality (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 5 - Allowance for Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-5-allowance-for-loan-losses-tables</Role>
      <ShortName>Note 5 - Allowance for Loan Losses (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 6 - FDIC Indemnification Asset (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-6-fdic-indemnification-asset-tables</Role>
      <ShortName>Note 6 - FDIC Indemnification Asset (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 7 - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-7-deposits-tables</Role>
      <ShortName>Note 7 - Deposits (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Disclosure - Note 8 - Borrowings (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-8-borrowings-tables</Role>
      <ShortName>Note 8 - Borrowings (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 9 - Derivative Instruments and Hedging Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-9-derivative-instruments-and-hedging-activities-tables</Role>
      <ShortName>Note 9 - Derivative Instruments and Hedging Activities (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Note 10 - Employee Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-10-employee-benefit-plans-tables</Role>
      <ShortName>Note 10 - Employee Benefit Plans (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 11 - Accumulated Other Comprehensive Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-11-accumulated-other-comprehensive-income-tables</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 12 - Fair Value (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-12-fair-value-tables</Role>
      <ShortName>Note 12 - Fair Value (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 13 - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-13-earnings-per-share-tables</Role>
      <ShortName>Note 13 - Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 14 - Litigation, Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-14-litigation-commitments-and-contingencies-tables</Role>
      <ShortName>Note 14 - Litigation, Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 1 - Basis of Presentation (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-1-basis-of-presentation-details-textual</Role>
      <ShortName>Note 1 - Basis of Presentation (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 2 - Investment Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-details-textual</Role>
      <ShortName>Note 2 - Investment Securities (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 2 - Investment Securities - Securities Available For Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-securities-available-for-sale-details</Role>
      <ShortName>Note 2 - Investment Securities - Securities Available For Sale (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 2 - Investment Securities - Securities Held to Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-securities-held-to-maturity-details</Role>
      <ShortName>Note 2 - Investment Securities - Securities Held to Maturity (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 2 - Investment Securities - Amortized Cost and Aggregate Fair Value of Available For Sale and Held to Maturity Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-amortized-cost-and-aggregate-fair-value-of-available-for-sale-and-held-to-maturity-securities-details</Role>
      <ShortName>Note 2 - Investment Securities - Amortized Cost and Aggregate Fair Value of Available For Sale and Held to Maturity Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>041 - Disclosure - Note 2 - Investment Securities - Available For Sale Securities in Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-available-for-sale-securities-in-continuous-unrealized-loss-position-details</Role>
      <ShortName>Note 2 - Investment Securities - Available For Sale Securities in Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>042 - Disclosure - Note 2 - Investment Securities - Held to Maturity Securities in Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-held-to-maturity-securities-in-continuous-unrealized-loss-position-details</Role>
      <ShortName>Note 2 - Investment Securities - Held to Maturity Securities in Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>043 - Disclosure - Note 2 - Investment Securities - Net Loss or Gain from Sale of Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-2-investment-securities-net-loss-or-gain-from-sale-of-securities-details</Role>
      <ShortName>Note 2 - Investment Securities - Net Loss or Gain from Sale of Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>044 - Disclosure - Note 3 - Loans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans-details-textual</Role>
      <ShortName>Note 3 - Loans (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>045 - Disclosure - Note 3 - Loans - Summary of Loans, Net of Unearned Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans-summary-of-loans-net-of-unearned-income-details</Role>
      <ShortName>Note 3 - Loans - Summary of Loans, Net of Unearned Income (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>046 - Disclosure - Note 3 - Loans - Covered Loan Portfolio, Disaggregated by Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans-covered-loan-portfolio-disaggregated-by-class-details</Role>
      <ShortName>Note 3 - Loans - Covered Loan Portfolio, Disaggregated by Class (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>047 - Disclosure - Note 3 - Loans - Carrying and Contractual Unpaid Principal Balance of PCI loans, by Acquisition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans-carrying-and-contractual-unpaid-principal-balance-of-pci-loans-by-acquisition-details</Role>
      <ShortName>Note 3 - Loans - Carrying and Contractual Unpaid Principal Balance of PCI loans, by Acquisition (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>048 - Disclosure - Note 3 - Loans - Activity in Accretable Yield on PCI loans, by Acquisition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-3-loans-activity-in-accretable-yield-on-pci-loans-by-acquisition-details</Role>
      <ShortName>Note 3 - Loans - Activity in Accretable Yield on PCI loans, by Acquisition (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>049 - Disclosure - Note 4 - Credit Quality (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-details-textual</Role>
      <ShortName>Note 4 - Credit Quality (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>050 - Disclosure - Note 4 - Credit Quality - Loans Held for Investment by Internal Credit Risk Grade (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-loans-held-for-investment-by-internal-credit-risk-grade-details</Role>
      <ShortName>Note 4 - Credit Quality - Loans Held for Investment by Internal Credit Risk Grade (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>051 - Disclosure - Note 4 - Credit Quality - Recorded Investment and Interest Income Recognized on Impaired Loans Excluding Purchased Credit Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-recorded-investment-and-interest-income-recognized-on-impaired-loans-excluding-purchased-credit-impaired-loans-details</Role>
      <ShortName>Note 4 - Credit Quality - Recorded Investment and Interest Income Recognized on Impaired Loans Excluding Purchased Credit Impaired Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>052 - Disclosure - Note 4 - Credit Quality - Average Annual Recorded Investment and Interest Income Recognized on Impaired Loans Excluding Purchased Credit Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-average-annual-recorded-investment-and-interest-income-recognized-on-impaired-loans-excluding-purchased-credit-impaired-loans-details</Role>
      <ShortName>Note 4 - Credit Quality - Average Annual Recorded Investment and Interest Income Recognized on Impaired Loans Excluding Purchased Credit Impaired Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>053 - Disclosure - Note 4 - Credit Quality - Information on Impaired PCI Loan Pools (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-information-on-impaired-pci-loan-pools-details</Role>
      <ShortName>Note 4 - Credit Quality - Information on Impaired PCI Loan Pools (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>054 - Disclosure - Note 4 - Credit Quality - Nonaccrual Loans by Loan Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-nonaccrual-loans-by-loan-class-details</Role>
      <ShortName>Note 4 - Credit Quality - Nonaccrual Loans by Loan Class (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>055 - Disclosure - Note 4 - Credit Quality - Aging of Past Due Loans by Loan Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-aging-of-past-due-loans-by-loan-class-details</Role>
      <ShortName>Note 4 - Credit Quality - Aging of Past Due Loans by Loan Class (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>056 - Disclosure - Note 4 - Credit Quality - Loans Modified as Troubled Debt Restructurings by Loan Class Segregated by Accrual Status (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-loans-modified-as-troubled-debt-restructurings-by-loan-class-segregated-by-accrual-status-details</Role>
      <ShortName>Note 4 - Credit Quality - Loans Modified as Troubled Debt Restructurings by Loan Class Segregated by Accrual Status (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>057 - Disclosure - Note 4 - Credit Quality - Balance and Interest Income Related to Impaired Loan Pools (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-balance-and-interest-income-related-to-impaired-loan-pools-details</Role>
      <ShortName>Note 4 - Credit Quality - Balance and Interest Income Related to Impaired Loan Pools (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>058 - Disclosure - Note 4 - Credit Quality - Summary of Information for OREO (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-4-credit-quality-summary-of-information-for-oreo-details</Role>
      <ShortName>Note 4 - Credit Quality - Summary of Information for OREO (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>059 - Disclosure - Note 5 - Allowance for Loan Losses - Allowance for Loan Losses, by Loan Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-5-allowance-for-loan-losses-allowance-for-loan-losses-by-loan-segment-details</Role>
      <ShortName>Note 5 - Allowance for Loan Losses - Allowance for Loan Losses, by Loan Segment (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>060 - Disclosure - Note 5 - Allowance for Loan Losses - Allowance for Loan Losses and Recorded Investment in Loans, Evaluated for Impairment Excluding PCI Loans, by Loan Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-5-allowance-for-loan-losses-allowance-for-loan-losses-and-recorded-investment-in-loans-evaluated-for-impairment-excluding-pci-loans-by-loan-class-details</Role>
      <ShortName>Note 5 - Allowance for Loan Losses - Allowance for Loan Losses and Recorded Investment in Loans, Evaluated for Impairment Excluding PCI Loans, by Loan Class (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>061 - Disclosure - Note 5 - Allowance for Loan Losses - Allowance for Loan Losses on PCI Loans and Recorded Investment in Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-5-allowance-for-loan-losses-allowance-for-loan-losses-on-pci-loans-and-recorded-investment-in-loans-details</Role>
      <ShortName>Note 5 - Allowance for Loan Losses - Allowance for Loan Losses on PCI Loans and Recorded Investment in Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>062 - Disclosure - Note 6 - FDIC Indemnification Asset (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-6-fdic-indemnification-asset-details-textual</Role>
      <ShortName>Note 6 - FDIC Indemnification Asset (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>063 - Disclosure - Note 6 - FDIC Indemnification Asset - Changes in Receivable from FDIC (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-6-fdic-indemnification-asset-changes-in-receivable-from-fdic-details</Role>
      <ShortName>Note 6 - FDIC Indemnification Asset - Changes in Receivable from FDIC (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>064 - Disclosure - Note 7 - Deposits - Components of Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-7-deposits-components-of-deposits-details</Role>
      <ShortName>Note 7 - Deposits - Components of Deposits (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>065 - Disclosure - Note 8 - Borrowings (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-8-borrowings-details-textual</Role>
      <ShortName>Note 8 - Borrowings (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>066 - Disclosure - Note 8 - Borrowings - Components of Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-8-borrowings-components-of-borrowings-details</Role>
      <ShortName>Note 8 - Borrowings - Components of Borrowings (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>067 - Disclosure - Note 8 - Borrowings - Remaining Contractual Maturities of Repurchased Agreements and FHLB Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-8-borrowings-remaining-contractual-maturities-of-repurchased-agreements-and-fhlb-borrowings-details</Role>
      <ShortName>Note 8 - Borrowings - Remaining Contractual Maturities of Repurchased Agreements and FHLB Borrowings (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>068 - Disclosure - Note 8 - Borrowings - Schedule of Remaining Contractual Maturities of Repurchase Agreements by Type of Collateral Pledged (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-8-borrowings-schedule-of-remaining-contractual-maturities-of-repurchase-agreements-by-type-of-collateral-pledged-details</Role>
      <ShortName>Note 8 - Borrowings - Schedule of Remaining Contractual Maturities of Repurchase Agreements by Type of Collateral Pledged (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>069 - Disclosure - Note 9 - Derivative Instruments and Hedging Activities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-9-derivative-instruments-and-hedging-activities-details-textual</Role>
      <ShortName>Note 9 - Derivative Instruments and Hedging Activities (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>070 - Disclosure - Note 9 - Derivative Instruments and Hedging Activities - Aggregate Contractual or Notional Amounts and Fair Value of Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-9-derivative-instruments-and-hedging-activities-aggregate-contractual-or-notional-amounts-and-fair-value-of-derivative-financial-instruments-details</Role>
      <ShortName>Note 9 - Derivative Instruments and Hedging Activities - Aggregate Contractual or Notional Amounts and Fair Value of Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>071 - Disclosure - Note 9 - Derivative Instruments and Hedging Activities - Effect of Derivative and Hedging Activity, on Consolidated Statements of Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-9-derivative-instruments-and-hedging-activities-effect-of-derivative-and-hedging-activity-on-consolidated-statements-of-income-details</Role>
      <ShortName>Note 9 - Derivative Instruments and Hedging Activities - Effect of Derivative and Hedging Activity, on Consolidated Statements of Income (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>072 - Disclosure - Note 10 - Employee Benefit Plans - Net Periodic Benefit Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-10-employee-benefit-plans-net-periodic-benefit-cost-details</Role>
      <ShortName>Note 10 - Employee Benefit Plans - Net Periodic Benefit Cost (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>073 - Disclosure - Note 11 - Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income, Net of Tax (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-11-accumulated-other-comprehensive-income-components-of-accumulated-other-comprehensive-income-net-of-tax-details</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income, Net of Tax (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>074 - Disclosure - Note 11 - Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-11-accumulated-other-comprehensive-income-reclassifications-out-of-accumulated-other-comprehensive-income-details</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>075 - Disclosure - Note 12 - Fair Value - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-12-fair-value-summary-of-financial-assets-and-liabilities-measured-at-fair-value-on-recurring-basis-details</Role>
      <ShortName>Note 12 - Fair Value - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>076 - Disclosure - Note 12 - Fair Value - Assets Measured at Fair Value on Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-12-fair-value-assets-measured-at-fair-value-on-nonrecurring-basis-details</Role>
      <ShortName>Note 12 - Fair Value - Assets Measured at Fair Value on Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>077 - Disclosure - Note 12 - Fair Value - Quantitative Information for Assets Measured at Fair Value on Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-12-fair-value-quantitative-information-for-assets-measured-at-fair-value-on-nonrecurring-basis-details</Role>
      <ShortName>Note 12 - Fair Value - Quantitative Information for Assets Measured at Fair Value on Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>078 - Disclosure - Note 12 - Fair Value - Carrying Amount and Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-12-fair-value-carrying-amount-and-fair-value-of-financial-instruments-details</Role>
      <ShortName>Note 12 - Fair Value - Carrying Amount and Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>079 - Disclosure - Note 13 - Earnings Per Share - Calculation for Basic and Diluted Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-13-earnings-per-share-calculation-for-basic-and-diluted-earnings-per-common-share-details</Role>
      <ShortName>Note 13 - Earnings Per Share - Calculation for Basic and Diluted Earnings Per Common Share (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="fcbc-20170331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>080 - Disclosure - Note 14 - Litigation, Commitments and Contingencies - Off-Balance Sheet Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fcbinc.com/20170331/role/statement-note-14-litigation-commitments-and-contingencies-offbalance-sheet-financial-instruments-details</Role>
      <ShortName>Note 14 - Litigation, Commitments and Contingencies - Off-Balance Sheet Financial Instruments (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>fcbc-20170331.xml</File>
    <File>fcbc-20170331.xsd</File>
    <File>fcbc-20170331_cal.xml</File>
    <File>fcbc-20170331_def.xml</File>
    <File>fcbc-20170331_lab.xml</File>
    <File>fcbc-20170331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
