<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>840</ContextCount>
  <ElementCount>318</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>98</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/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="fcbc20250630_10q.htm">
      <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.firstcommunitybank.com/20250630/role/statement-note-1-basis-of-presentation</Role>
      <ShortName>Note 1 - Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 2 - Debt Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities</Role>
      <ShortName>Note 2 - Debt Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 3 - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-3-loans</Role>
      <ShortName>Note 3 - Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 4 - Credit Quality</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality</Role>
      <ShortName>Note 4 - Credit Quality</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 5 - Allowance for Credit Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-5-allowance-for-credit-losses</Role>
      <ShortName>Note 5 - Allowance for Credit Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 6 - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-6-deposits</Role>
      <ShortName>Note 6 - Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 7 - Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-7-borrowings</Role>
      <ShortName>Note 7 - Borrowings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 8 - Derivative Instruments and Hedging Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-8-derivative-instruments-and-hedging-activities</Role>
      <ShortName>Note 8 - Derivative Instruments and Hedging Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 9 - Employee Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-9-employee-benefit-plans</Role>
      <ShortName>Note 9 - Employee Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 10 - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-10-earnings-per-share</Role>
      <ShortName>Note 10 - Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 11 - Accumulated Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 12 - Fair Value</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-12-fair-value</Role>
      <ShortName>Note 12 - Fair Value</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 13 - Litigation, Commitments, and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-13-litigation-commitments-and-contingencies</Role>
      <ShortName>Note 13 - Litigation, Commitments, and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 14 - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-14-segment-information</Role>
      <ShortName>Note 14 - Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 15 - Subsequent Event</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-15-subsequent-event</Role>
      <ShortName>Note 15 - Subsequent Event</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995469 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>995470 - Disclosure - Note 2 - Debt Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities-tables</Role>
      <ShortName>Note 2 - Debt Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>995471 - Disclosure - Note 3 - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-3-loans-tables</Role>
      <ShortName>Note 3 - Loans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-3-loans</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>995472 - Disclosure - Note 4 - Credit Quality (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-tables</Role>
      <ShortName>Note 4 - Credit Quality (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>995473 - Disclosure - Note 5 - Allowance for Credit Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-5-allowance-for-credit-losses-tables</Role>
      <ShortName>Note 5 - Allowance for Credit Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-5-allowance-for-credit-losses</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>995474 - Disclosure - Note 6 - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-6-deposits-tables</Role>
      <ShortName>Note 6 - Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-6-deposits</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>995475 - Disclosure - Note 7 - Borrowings (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-7-borrowings-tables</Role>
      <ShortName>Note 7 - Borrowings (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-7-borrowings</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>995476 - Disclosure - Note 8 - Derivative Instruments and Hedging Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-8-derivative-instruments-and-hedging-activities-tables</Role>
      <ShortName>Note 8 - Derivative Instruments and Hedging Activities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-8-derivative-instruments-and-hedging-activities</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>995477 - Disclosure - Note 9 - Employee Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-9-employee-benefit-plans-tables</Role>
      <ShortName>Note 9 - Employee Benefit Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-9-employee-benefit-plans</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>995478 - Disclosure - Note 10 - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-10-earnings-per-share-tables</Role>
      <ShortName>Note 10 - Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-10-earnings-per-share</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>995479 - Disclosure - Note 11 - Accumulated Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss-tables</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income (Loss) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>995480 - Disclosure - Note 12 - Fair Value (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-12-fair-value-tables</Role>
      <ShortName>Note 12 - Fair Value (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-12-fair-value</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>995481 - Disclosure - Note 13 - Litigation, Commitments, and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-13-litigation-commitments-and-contingencies-tables</Role>
      <ShortName>Note 13 - Litigation, Commitments, and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-13-litigation-commitments-and-contingencies</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>995482 - Disclosure - Note 2 - Debt Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities-details-textual</Role>
      <ShortName>Note 2 - Debt Securities (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities-tables</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>995483 - Disclosure - Note 2 - Debt Securities - Securities Available-for-sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities-securities-availableforsale-details</Role>
      <ShortName>Note 2 - Debt Securities - Securities Available-for-sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>995484 - Disclosure - Note 2 - Debt Securities - Securities by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities-securities-by-contractual-maturity-details</Role>
      <ShortName>Note 2 - Debt Securities - Securities by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>995485 - Disclosure - Note 2 - Debt Securities - Available For Sale Securities in Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-2-debt-securities-available-for-sale-securities-in-continuous-unrealized-loss-position-details</Role>
      <ShortName>Note 2 - Debt Securities - Available For Sale Securities in Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>995486 - Disclosure - Note 3 - Loans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-3-loans-details-textual</Role>
      <ShortName>Note 3 - Loans (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-3-loans-tables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>995487 - Disclosure - Note 3 - Loans - Loans by Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-3-loans-loans-by-class-details</Role>
      <ShortName>Note 3 - Loans - Loans by Class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>995488 - Disclosure - Note 4 - Credit Quality (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-details-textual</Role>
      <ShortName>Note 4 - Credit Quality (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-tables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>995489 - Disclosure - Note 4 - Credit Quality - Loans by Credit Quality (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-loans-by-credit-quality-details</Role>
      <ShortName>Note 4 - Credit Quality - Loans by Credit Quality (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>995490 - Disclosure - Note 4 - Credit Quality - Nonaccrual Loans by Loan Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/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>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>995491 - Disclosure - Note 4 - Credit Quality - Aging of Past Due Loans by Loan Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/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>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>995492 - Disclosure - Note 4 - Credit Quality - Collateral Dependent Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-collateral-dependent-loans-details</Role>
      <ShortName>Note 4 - Credit Quality - Collateral Dependent Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>995493 - Disclosure - Note 4 - Credit Quality - Loans Modified as Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-loans-modified-as-troubled-debt-restructurings-details</Role>
      <ShortName>Note 4 - Credit Quality - Loans Modified as Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>995494 - Disclosure - Note 4 - Credit Quality - Other Real Estate Owned (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-4-credit-quality-other-real-estate-owned-details</Role>
      <ShortName>Note 4 - Credit Quality - Other Real Estate Owned (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>995495 - Disclosure - Note 5 - Allowance for Credit Losses - Changes in Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-5-allowance-for-credit-losses-changes-in-allowance-for-loan-losses-details</Role>
      <ShortName>Note 5 - Allowance for Credit Losses - Changes in Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>995496 - Disclosure - Note 6 - Deposits - Components of Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-6-deposits-components-of-deposits-details</Role>
      <ShortName>Note 6 - Deposits - Components of Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>995497 - Disclosure - Note 7 - Borrowings (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-7-borrowings-details-textual</Role>
      <ShortName>Note 7 - Borrowings (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-7-borrowings-tables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>995498 - Disclosure - Note 7 - Borrowings - Components of Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-7-borrowings-components-of-borrowings-details</Role>
      <ShortName>Note 7 - Borrowings - Components of Borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>995499 - Disclosure - Note 8 - Derivative Instruments and Hedging Activities - Notional or Contractual Amounts and Fair Values of Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-8-derivative-instruments-and-hedging-activities-notional-or-contractual-amounts-and-fair-values-of-derivative-financial-instruments-details</Role>
      <ShortName>Note 8 - Derivative Instruments and Hedging Activities - Notional or Contractual Amounts and Fair Values of Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>995500 - Disclosure - Note 8 - Derivative Instruments and Hedging Activities - Effect of Derivative and Hedging Activity, on Consolidated Statements of Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-8-derivative-instruments-and-hedging-activities-effect-of-derivative-and-hedging-activity-on-consolidated-statements-of-income-details</Role>
      <ShortName>Note 8 - Derivative Instruments and Hedging Activities - Effect of Derivative and Hedging Activity, on Consolidated Statements of Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>995501 - Disclosure - Note 9 - Employee Benefit Plans - Components of Net Periodic Pension Cost and Assumed Discount Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-9-employee-benefit-plans-components-of-net-periodic-pension-cost-and-assumed-discount-rate-details</Role>
      <ShortName>Note 9 - Employee Benefit Plans - Components of Net Periodic Pension Cost and Assumed Discount Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>995502 - Disclosure - Note 10 - Earnings Per Share - Basic and Diluted Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-10-earnings-per-share-basic-and-diluted-earnings-per-common-share-details</Role>
      <ShortName>Note 10 - Earnings Per Share - Basic and Diluted Earnings Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>995503 - Disclosure - Note 11 - Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income, Net of Tax (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss-components-of-accumulated-other-comprehensive-income-net-of-tax-details</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income, Net of Tax (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss-tables</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>995504 - Disclosure - Note 11 - Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss-reclassifications-out-of-accumulated-other-comprehensive-income-loss-details</Role>
      <ShortName>Note 11 - Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-11-accumulated-other-comprehensive-income-loss-tables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>995505 - Disclosure - Note 12 - Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-12-fair-value-assets-and-liabilities-measured-at-fair-value-on-recurring-basis-details</Role>
      <ShortName>Note 12 - Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>995506 - Disclosure - Note 12 - Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-12-fair-value-assets-and-liabilities-measured-at-fair-value-on-recurring-basis-details-parentheticals</Role>
      <ShortName>Note 12 - Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) (Parentheticals)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>995507 - Disclosure - Note 12 - Fair Value - Assets Measured at Fair Value on Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/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>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>995508 - Disclosure - Note 12 - Fair Value - Quantitative Information for Assets Measured at Fair Value on Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/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>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>995509 - Disclosure - Note 12 - Fair Value - Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-12-fair-value-financial-instruments-details</Role>
      <ShortName>Note 12 - Fair Value - Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>995510 - Disclosure - Note 13 - Litigation, Commitments, and Contingencies - Off-balance Sheet Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-13-litigation-commitments-and-contingencies-offbalance-sheet-financial-instruments-details</Role>
      <ShortName>Note 13 - Litigation, Commitments, and Contingencies - Off-balance Sheet Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>995511 - Disclosure - Note 14 - Segment Information (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-14-segment-information-details-textual</Role>
      <ShortName>Note 14 - Segment Information (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-14-segment-information</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="fcbc20250630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>995512 - Disclosure - Note 15 - Subsequent Event (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.firstcommunitybank.com/20250630/role/statement-note-15-subsequent-event-details-textual</Role>
      <ShortName>Note 15 - Subsequent Event (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.firstcommunitybank.com/20250630/role/statement-note-15-subsequent-event</ParentRole>
      <Position>68</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-20250630.xsd</File>
    <File>fcbc-20250630_cal.xml</File>
    <File>fcbc-20250630_def.xml</File>
    <File>fcbc-20250630_lab.xml</File>
    <File>fcbc-20250630_pre.xml</File>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="fcbc20250630_10q.htm">fcbc20250630_10q.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="32">http://fasb.org/srt/2025</BaseTaxonomy>
    <BaseTaxonomy items="2947">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="29">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="5">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
