<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>631</ContextCount>
  <ElementCount>410</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>78</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="cbfv-20190331.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.communitybank.tv/20190331/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Consolidated Statement of Financial Condition (Current Period Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-financial-condition-current-period-unaudited</Role>
      <ShortName>Consolidated Statement of Financial Condition (Current Period Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Consolidated Statement of Financial Condition (Current Period Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-financial-condition-current-period-unaudited-parentheticals</Role>
      <ShortName>Consolidated Statement of Financial Condition (Current Period Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Consolidated Statement of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-income-unaudited-</Role>
      <ShortName>Consolidated Statement of Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Consolidated Statement of Comprehensive Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-comprehensive-income-unaudited</Role>
      <ShortName>Consolidated Statement of Comprehensive Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Consolidated Statement of Comprehensive Income (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-comprehensive-income-unaudited-parentheticals</Role>
      <ShortName>Consolidated Statement of Comprehensive Income (Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Statement - Consolidated Statement of Changes in Stockholders' Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-changes-in-stockholders-equity-unaudited-</Role>
      <ShortName>Consolidated Statement of Changes in Stockholders' Equity (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Statement - Consolidated Statement of Changes in Stockholders' Equity (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-changes-in-stockholders-equity-unaudited-parentheticals</Role>
      <ShortName>Consolidated Statement of Changes in Stockholders' Equity (Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Statement - Consolidated Statement of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-cash-flows-unaudited</Role>
      <ShortName>Consolidated Statement of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Statement - Consolidated Statement of Cash Flows (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-consolidated-statement-of-cash-flows-unaudited-parentheticals</Role>
      <ShortName>Consolidated Statement of Cash Flows (Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 1 - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-1-summary-of-significant-accounting-policies</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 2 - Merger</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-2-merger</Role>
      <ShortName>Note 2 - Merger</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 3 - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-3-earnings-per-share</Role>
      <ShortName>Note 3 - Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 4 - Revenue Recognition From Contracts With Customers</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-4-revenue-recognition-from-contracts-with-customers</Role>
      <ShortName>Note 4 - Revenue Recognition From Contracts With Customers</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 5 - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities</Role>
      <ShortName>Note 5 - Investment Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 7 - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-7-leases</Role>
      <ShortName>Note 7 - Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 8 - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-8-deposits</Role>
      <ShortName>Note 8 - Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 9 - Short-term Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-9-shortterm-borrowings</Role>
      <ShortName>Note 9 - Short-term Borrowings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 10 - Other Borrowed Funds</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-10-other-borrowed-funds</Role>
      <ShortName>Note 10 - Other Borrowed Funds</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 11 - Commitments and Contingent Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-11-commitments-and-contingent-liabilities</Role>
      <ShortName>Note 11 - Commitments and Contingent Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 12 - Fair Value Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure</Role>
      <ShortName>Note 12 - Fair Value Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 13 - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-13-income-taxes</Role>
      <ShortName>Note 13 - Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 14 - Other Noninterest Expense</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-14-other-noninterest-expense</Role>
      <ShortName>Note 14 - Other Noninterest Expense</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Note 15 - Segment and Related Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-15-segment-and-related-information-</Role>
      <ShortName>Note 15 - Segment and Related Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-1-summary-of-significant-accounting-policies</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 2 - Merger (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-2-merger-tables</Role>
      <ShortName>Note 2 - Merger (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-2-merger</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 3 - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-3-earnings-per-share-tables</Role>
      <ShortName>Note 3 - Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-3-earnings-per-share</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 4 - Revenue Recognition From Contracts With Customers (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-4-revenue-recognition-from-contracts-with-customers-tables</Role>
      <ShortName>Note 4 - Revenue Recognition From Contracts With Customers (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-4-revenue-recognition-from-contracts-with-customers</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Disclosure - Note 5 - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities-tables</Role>
      <ShortName>Note 5 - Investment Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-tables</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Note 7 - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-7-leases-tables</Role>
      <ShortName>Note 7 - Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-7-leases</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 8 - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-8-deposits-tables</Role>
      <ShortName>Note 8 - Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-8-deposits</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 9 - Short-term Borrowings (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-9-shortterm-borrowings-tables</Role>
      <ShortName>Note 9 - Short-term Borrowings (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-9-shortterm-borrowings</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 10 - Other Borrowed Funds (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-10-other-borrowed-funds-tables</Role>
      <ShortName>Note 10 - Other Borrowed Funds (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-10-other-borrowed-funds</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 11 - Commitments and Contingent Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-11-commitments-and-contingent-liabilities-tables</Role>
      <ShortName>Note 11 - Commitments and Contingent Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-11-commitments-and-contingent-liabilities</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 12 - Fair Value Disclosure (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure-tables</Role>
      <ShortName>Note 12 - Fair Value Disclosure (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 13 - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-13-income-taxes-tables</Role>
      <ShortName>Note 13 - Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-13-income-taxes</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 14 - Other Noninterest Expense (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-14-other-noninterest-expense-tables</Role>
      <ShortName>Note 14 - Other Noninterest Expense (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-14-other-noninterest-expense</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 15 - Segment and Related Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-15-segment-and-related-information-tables</Role>
      <ShortName>Note 15 - Segment and Related Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-15-segment-and-related-information-</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 1 - Summary of Significant Accounting Policies (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-1-summary-of-significant-accounting-policies-details-textual</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>041 - Disclosure - Note 2 - Merger (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-2-merger-details-textual</Role>
      <ShortName>Note 2 - Merger (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-2-merger-tables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>042 - Disclosure - Note 2 - Merger - Fair Value of the Assets Acquired and Liabilities Assumed in the FWVB Merger (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-2-merger-fair-value-of-the-assets-acquired-and-liabilities-assumed-in-the-fwvb-merger-details</Role>
      <ShortName>Note 2 - Merger - Fair Value of the Assets Acquired and Liabilities Assumed in the FWVB Merger (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>043 - Disclosure - Note 3 - Earnings Per Share (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-3-earnings-per-share-details-textual</Role>
      <ShortName>Note 3 - Earnings Per Share (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-3-earnings-per-share-tables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>044 - Disclosure - Note 3 - Earnings Per Share - Basic and Diluted Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-3-earnings-per-share-basic-and-diluted-earnings-per-common-share-details</Role>
      <ShortName>Note 3 - Earnings Per Share - Basic and Diluted Earnings Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>045 - Disclosure - Note 4 - Revenue Recognition From Contracts With Customers (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-4-revenue-recognition-from-contracts-with-customers-details-textual</Role>
      <ShortName>Note 4 - Revenue Recognition From Contracts With Customers (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-4-revenue-recognition-from-contracts-with-customers-tables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>046 - Disclosure - Note 4 - Revenue Recognition From Contracts With Customers - Impact of the Accounting Standard On Revenue Streams (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-4-revenue-recognition-from-contracts-with-customers-impact-of-the-accounting-standard-on-revenue-streams-details</Role>
      <ShortName>Note 4 - Revenue Recognition From Contracts With Customers - Impact of the Accounting Standard On Revenue Streams (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>047 - Disclosure - Note 5 - Investment Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities-details-textual</Role>
      <ShortName>Note 5 - Investment Securities (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities-tables</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>048 - Disclosure - Note 5 - Investment Securities - Amortized Cost and Fair Value of Investment Securities Available-for-sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities-amortized-cost-and-fair-value-of-investment-securities-availableforsale-details</Role>
      <ShortName>Note 5 - Investment Securities - Amortized Cost and Fair Value of Investment Securities Available-for-sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>049 - Disclosure - Note 5 - Investment Securities - Gross Unrealized Losses and Fair Value by Investment Category and Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities-gross-unrealized-losses-and-fair-value-by-investment-category-and-continuous-unrealized-loss-position-details</Role>
      <ShortName>Note 5 - Investment Securities - Gross Unrealized Losses and Fair Value by Investment Category and Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>050 - Disclosure - Note 5 - Investment Securities - Maturities of Investment Securities Available-for-sale and Held-to-maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-5-investment-securities-maturities-of-investment-securities-availableforsale-and-heldtomaturity-details</Role>
      <ShortName>Note 5 - Investment Securities - Maturities of Investment Securities Available-for-sale and Held-to-maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>051 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-details-textual</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-tables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>052 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Composition of Loan Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-composition-of-loan-portfolio-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Composition of Loan Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>053 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Credit Quality Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-credit-quality-information-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Credit Quality Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>054 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Loans by Aging Categories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-loans-by-aging-categories-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Loans by Aging Categories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>055 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Nonperforming Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-nonperforming-assets-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Nonperforming Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>056 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Loans Classified as TDRs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-loans-classified-as-tdrs-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Loans Classified as TDRs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>057 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-impaired-loans-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Impaired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>058 - Disclosure - Note 6 - Loans and Related Allowance for Loan Loss - Activity in the Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-loss-activity-in-the-allowance-for-loan-losses-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Loss - Activity in the Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>059 - Disclosure - Note 6 - Loans and Related Allowance for Loan Losses - Accretable Discount on Loans Acquired at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-losses-accretable-discount-on-loans-acquired-at-fair-value-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Losses - Accretable Discount on Loans Acquired at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>060 - Disclosure - Note 6 - Loans and Related Allowance for Loan Losses - Loans Summarized by Individually Evaluated for Impairment and Collectively Evaluated for Potential Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-6-loans-and-related-allowance-for-loan-losses-loans-summarized-by-individually-evaluated-for-impairment-and-collectively-evaluated-for-potential-losses-details</Role>
      <ShortName>Note 6 - Loans and Related Allowance for Loan Losses - Loans Summarized by Individually Evaluated for Impairment and Collectively Evaluated for Potential Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>061 - Disclosure - Note 7 - Leases - Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-7-leases-operating-leases-details</Role>
      <ShortName>Note 7 - Leases - Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>062 - Disclosure - Note 7 - Leases - Maturity of Operating Lease (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-7-leases-maturity-of-operating-lease-details</Role>
      <ShortName>Note 7 - Leases - Maturity of Operating Lease (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>063 - Disclosure - Note 8 - Deposits (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-8-deposits-details-textual</Role>
      <ShortName>Note 8 - Deposits (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-8-deposits-tables</ParentRole>
      <Position>64</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>064 - Disclosure - Note 8 - Deposits - Maturities of Time Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-8-deposits-maturities-of-time-deposits-details</Role>
      <ShortName>Note 8 - Deposits - Maturities of Time Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>065 - Disclosure - Note 9 - Short-term Borrowings - Federal Funds Purchased and Short-term Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-9-shortterm-borrowings-federal-funds-purchased-and-shortterm-borrowings-details</Role>
      <ShortName>Note 9 - Short-term Borrowings - Federal Funds Purchased and Short-term Borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>066 - Disclosure - Note 10 - Other Borrowed Funds (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-10-other-borrowed-funds-details-textual</Role>
      <ShortName>Note 10 - Other Borrowed Funds (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-10-other-borrowed-funds-tables</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>067 - Disclosure - Note 10 - Other Borrowed Funds - Federal Home Loan Bank Advances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-10-other-borrowed-funds-federal-home-loan-bank-advances-details</Role>
      <ShortName>Note 10 - Other Borrowed Funds - Federal Home Loan Bank Advances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>068 - Disclosure - Note 11 - Commitments and Contingent Liabilities - Unused and Available Credit Balances of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-11-commitments-and-contingent-liabilities-unused-and-available-credit-balances-of-financial-instruments-details</Role>
      <ShortName>Note 11 - Commitments and Contingent Liabilities - Unused and Available Credit Balances of Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>069 - Disclosure - Note 12 - Fair Value Disclosure (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure-details-textual</Role>
      <ShortName>Note 12 - Fair Value Disclosure (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure-tables</ParentRole>
      <Position>70</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>070 - Disclosure - Note 12 - Fair Value Disclosure - Assets and Liabilities Reported Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure-assets-and-liabilities-reported-fair-value-details</Role>
      <ShortName>Note 12 - Fair Value Disclosure - Assets and Liabilities Reported Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>071 - Disclosure - Note 12 - Fair Value Disclosure - Significant Unobservable Inputs Used in the Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure-significant-unobservable-inputs-used-in-the-fair-value-measurements-details</Role>
      <ShortName>Note 12 - Fair Value Disclosure - Significant Unobservable Inputs Used in the Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>072 - Disclosure - Note 12 - Fair Value Disclosure - Estimated Fair Value of the Company's Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-12-fair-value-disclosure-estimated-fair-value-of-the-companys-financial-instruments-details</Role>
      <ShortName>Note 12 - Fair Value Disclosure - Estimated Fair Value of the Company's Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>073 - Disclosure - Note 13 - Income Taxes (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-13-income-taxes-details-textual</Role>
      <ShortName>Note 13 - Income Taxes (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-13-income-taxes-tables</ParentRole>
      <Position>74</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>074 - Disclosure - Note 13 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-13-income-taxes-summary-of-deferred-tax-assets-and-liabilities-details</Role>
      <ShortName>Note 13 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>075 - Disclosure - Note 14 - Other Noninterest Expense - Components of Other Noninterest Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-14-other-noninterest-expense-components-of-other-noninterest-expense-details</Role>
      <ShortName>Note 14 - Other Noninterest Expense - Components of Other Noninterest Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>076 - Disclosure - Note 15 - Segment and Related Information (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-15-segment-and-related-information-details-textual</Role>
      <ShortName>Note 15 - Segment and Related Information (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.communitybank.tv/20190331/role/statement-note-15-segment-and-related-information-tables</ParentRole>
      <Position>77</Position>
    </Report>
    <Report instance="cbfv-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>077 - Disclosure - Note 15 - Segment and Related Information - Reconciliation of Financial Data from Segments to Consolidated (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.communitybank.tv/20190331/role/statement-note-15-segment-and-related-information-reconciliation-of-financial-data-from-segments-to-consolidated-details</Role>
      <ShortName>Note 15 - Segment and Related Information - Reconciliation of Financial Data from Segments to Consolidated (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>cbfv-20190331.xml</File>
    <File>cbfv-20190331.xsd</File>
    <File>cbfv-20190331_cal.xml</File>
    <File>cbfv-20190331_def.xml</File>
    <File>cbfv-20190331_lab.xml</File>
    <File>cbfv-20190331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
