<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.21.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>448</ContextCount>
  <ElementCount>472</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>81</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/StatementCondensedConsolidatedBalanceSheets</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/StatementCondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/StatementCondensedConsolidatedStatementsOfIncome</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/StatementCondensedConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/StatementCondensedConsolidatedStatementOfChangesInShareholdersEquity</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00500 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/StatementCondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>10101 - Disclosure - BASIS OF PRESENTATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBasisOfPresentation</Role>
      <ShortName>BASIS OF PRESENTATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10201 - Disclosure - ACCOUNTING GUIDANCE NOT YET EFFECTIVE AND ADOPTED ACCOUNTING GUIDANCE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAccountingGuidanceNotYetEffectiveAndAdoptedAccountingGuidance</Role>
      <ShortName>ACCOUNTING GUIDANCE NOT YET EFFECTIVE AND ADOPTED ACCOUNTING GUIDANCE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10301 - Disclosure - ACQUISITIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitions</Role>
      <ShortName>ACQUISITIONS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10401 - Disclosure - INVESTMENT SECURITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecurities</Role>
      <ShortName>INVESTMENT SECURITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10501 - Disclosure - LOANS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoans</Role>
      <ShortName>LOANS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10601 - Disclosure - ALLOWANCE FOR LOAN LOSSES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAllowanceForLoanLosses</Role>
      <ShortName>ALLOWANCE FOR LOAN LOSSES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10701 - Disclosure - PREMISES AND EQUIPMENT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosurePremisesAndEquipment</Role>
      <ShortName>PREMISES AND EQUIPMENT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10801 - Disclosure - LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeases</Role>
      <ShortName>LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10901 - Disclosure - GOODWILL AND INTANGIBLE ASSETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssets</Role>
      <ShortName>GOODWILL AND INTANGIBLE ASSETS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>11001 - Disclosure - INTEREST RECEIVABLE AND OTHER ASSETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInterestReceivableAndOtherAssets</Role>
      <ShortName>INTEREST RECEIVABLE AND OTHER ASSETS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11101 - Disclosure - DEPOSITS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureDeposits</Role>
      <ShortName>DEPOSITS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11201 - Disclosure - BORROWINGS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBorrowings</Role>
      <ShortName>BORROWINGS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11301 - Disclosure - INTEREST PAYABLE AND OTHER LIABILITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInterestPayableAndOtherLiabilities</Role>
      <ShortName>INTEREST PAYABLE AND OTHER LIABILITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11401 - Disclosure - OTHER EXPENSES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureOtherExpenses</Role>
      <ShortName>OTHER EXPENSES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11501 - Disclosure - EQUITY INCENTIVE PLANS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlans</Role>
      <ShortName>EQUITY INCENTIVE PLANS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11601 - Disclosure - FAIR VALUE MEASUREMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>FAIR VALUE MEASUREMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11701 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueOfFinancialInstruments</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11801 - Disclosure - COMMITMENTS AND CONTINGENCIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>30303 - Disclosure - ACQUISITIONS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitionsTables</Role>
      <ShortName>ACQUISITIONS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureAcquisitions</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>30403 - Disclosure - INVESTMENT SECURITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecuritiesTables</Role>
      <ShortName>INVESTMENT SECURITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecurities</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>30503 - Disclosure - LOANS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansTables</Role>
      <ShortName>LOANS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureLoans</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>30603 - Disclosure - ALLOWANCE FOR LOAN LOSSES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAllowanceForLoanLossesTables</Role>
      <ShortName>ALLOWANCE FOR LOAN LOSSES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureAllowanceForLoanLosses</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>30703 - Disclosure - PREMISES AND EQUIPMENT (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosurePremisesAndEquipmentTables</Role>
      <ShortName>PREMISES AND EQUIPMENT (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosurePremisesAndEquipment</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30803 - Disclosure - LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeasesTables</Role>
      <ShortName>LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureLeases</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30903 - Disclosure - GOODWILL AND INTANGIBLE ASSETS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssetsTables</Role>
      <ShortName>GOODWILL AND INTANGIBLE ASSETS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssets</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>31003 - Disclosure - INTEREST RECEIVABLE AND OTHER ASSETS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInterestReceivableAndOtherAssetsTables</Role>
      <ShortName>INTEREST RECEIVABLE AND OTHER ASSETS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureInterestReceivableAndOtherAssets</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>31103 - Disclosure - DEPOSITS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureDepositsTables</Role>
      <ShortName>DEPOSITS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureDeposits</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>31303 - Disclosure - INTEREST PAYABLE AND OTHER LIABILITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInterestPayableAndOtherLiabilitiesTables</Role>
      <ShortName>INTEREST PAYABLE AND OTHER LIABILITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureInterestPayableAndOtherLiabilities</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>31403 - Disclosure - OTHER EXPENSES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureOtherExpensesTables</Role>
      <ShortName>OTHER EXPENSES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureOtherExpenses</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>31503 - Disclosure - EQUITY INCENTIVE PLANS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlansTables</Role>
      <ShortName>EQUITY INCENTIVE PLANS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlans</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>31603 - Disclosure - FAIR VALUE MEASUREMENT (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueMeasurementTables</Role>
      <ShortName>FAIR VALUE MEASUREMENT (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>31703 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueOfFinancialInstrumentsTables</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureFairValueOfFinancialInstruments</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>31803 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>40101 - Disclosure - BASIS OF PRESENTATION - General Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBasisOfPresentationGeneralInformationDetails</Role>
      <ShortName>BASIS OF PRESENTATION - General Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>40102 - Disclosure - BASIS OF PRESENTATION - Business Combinations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBasisOfPresentationBusinessCombinationsDetails</Role>
      <ShortName>BASIS OF PRESENTATION - Business Combinations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>40201 - Disclosure - ACCOUNTING GUIDANCE NOT YET EFFECTIVE AND ADOPTED ACCOUNTING GUIDANCE (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAccountingGuidanceNotYetEffectiveAndAdoptedAccountingGuidanceDetails</Role>
      <ShortName>ACCOUNTING GUIDANCE NOT YET EFFECTIVE AND ADOPTED ACCOUNTING GUIDANCE (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureAccountingGuidanceNotYetEffectiveAndAdoptedAccountingGuidance</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>40301 - Disclosure - ACQUISITIONS - General Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitionsGeneralInformationDetails</Role>
      <ShortName>ACQUISITIONS - General Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>40302 - Disclosure - ACQUISITIONS - Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitionsAssetsAcquiredAndLiabilitiesAssumedDetails</Role>
      <ShortName>ACQUISITIONS - Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>40303 - Disclosure - ACQUISITIONS - Consideration Transferred (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitionsConsiderationTransferredDetails</Role>
      <ShortName>ACQUISITIONS - Consideration Transferred (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>40304 - Disclosure - ACQUISITIONS - Pro Forma (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitionsProFormaDetails</Role>
      <ShortName>ACQUISITIONS - Pro Forma (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>40305 - Disclosure - ACQUISITIONS - Acquisition Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAcquisitionsAcquisitionExpensesDetails</Role>
      <ShortName>ACQUISITIONS - Acquisition Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>40401 - Disclosure - INVESTMENT SECURITIES - Amortized Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecuritiesAmortizedCostDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Amortized Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>40402 - Disclosure - INVESTMENT SECURITIES - Realized Gains (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecuritiesRealizedGainsDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Realized Gains (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>40403 - Disclosure - INVESTMENT SECURITIES - Estimated Fair Value and Gross Unrealized Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecuritiesEstimatedFairValueAndGrossUnrealizedLossesDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Estimated Fair Value and Gross Unrealized Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>40404 - Disclosure - INVESTMENT SECURITIES - Unrealized Loss Positions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecuritiesUnrealizedLossPositionsDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Unrealized Loss Positions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>40405 - Disclosure - INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInvestmentSecuritiesAmortizedCostAndEstimatedFairValueOfAvailableForSaleSecuritiesByContractualMaturityDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>40501 - Disclosure - LOANS - Loan Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansLoanPortfolioDetails</Role>
      <ShortName>LOANS - Loan Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>40502 - Disclosure - LOANS - Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansImpairedLoansDetails</Role>
      <ShortName>LOANS - Impaired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>40503 - Disclosure - LOANS - Troubled Debt Restructurings, Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansTroubledDebtRestructuringsAdditionalInformationDetails</Role>
      <ShortName>LOANS - Troubled Debt Restructurings, Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>40504 - Disclosure - LOANS - Troubled Debt Restructurings, Modified as TDR Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansTroubledDebtRestructuringsModifiedAsTdrLoansDetails</Role>
      <ShortName>LOANS - Troubled Debt Restructurings, Modified as TDR Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>40505 - Disclosure - LOANS - Risk Grade (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansRiskGradeDetails</Role>
      <ShortName>LOANS - Risk Grade (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>40506 - Disclosure - LOANS - Aging - Tabular Disclosure (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansAgingTabularDisclosureDetails</Role>
      <ShortName>LOANS - Aging - Tabular Disclosure (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>40507 - Disclosure - LOANS - Nonaccrual Loans - Guaranteed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansNonaccrualLoansGuaranteedDetails</Role>
      <ShortName>LOANS - Nonaccrual Loans - Guaranteed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>40508 - Disclosure - LOANS - Nonaccrual Loans - Aging (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansNonaccrualLoansAgingDetails</Role>
      <ShortName>LOANS - Nonaccrual Loans - Aging (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>40509 - Disclosure - LOANS - Nonaccrual Loans - General Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansNonaccrualLoansGeneralInformationDetails</Role>
      <ShortName>LOANS - Nonaccrual Loans - General Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>40510 - Disclosure - LOANS - PCI Loans - Unpaid Balance and Carrying Amount (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansPciLoansUnpaidBalanceAndCarryingAmountDetails</Role>
      <ShortName>LOANS - PCI Loans - Unpaid Balance and Carrying Amount (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>40511 - Disclosure - LOANS - PCI Loans - Accretable Yield - Roll Forward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLoansPciLoansAccretableYieldRollForwardDetails</Role>
      <ShortName>LOANS - PCI Loans - Accretable Yield - Roll Forward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>40601 - Disclosure - ALLOWANCE FOR LOAN LOSSES - Roll Forward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAllowanceForLoanLossesRollForwardDetails</Role>
      <ShortName>ALLOWANCE FOR LOAN LOSSES - Roll Forward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>40602 - Disclosure - ALLOWANCE FOR LOAN LOSSES - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureAllowanceForLoanLossesAdditionalInformationDetails</Role>
      <ShortName>ALLOWANCE FOR LOAN LOSSES - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>40701 - Disclosure - PREMISES AND EQUIPMENT - Tabular Disclosure (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosurePremisesAndEquipmentTabularDisclosureDetails</Role>
      <ShortName>PREMISES AND EQUIPMENT - Tabular Disclosure (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>40702 - Disclosure - PREMISES AND EQUIPMENT - Depreciation and Amortization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosurePremisesAndEquipmentDepreciationAndAmortizationDetails</Role>
      <ShortName>PREMISES AND EQUIPMENT - Depreciation and Amortization (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>40801 - Disclosure - LEASES - General Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeasesGeneralInformationDetails</Role>
      <ShortName>LEASES - General Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>40802 - Disclosure - LEASES - Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeasesMaturityDetails</Role>
      <ShortName>LEASES - Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>40803 - Disclosure - LEASES - Gross Difference (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeasesGrossDifferenceDetails</Role>
      <ShortName>LEASES - Gross Difference (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>40804 - Disclosure - LEASES - Weighted Average Operating Lease Term and Discount Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeasesWeightedAverageOperatingLeaseTermAndDiscountRateDetails</Role>
      <ShortName>LEASES - Weighted Average Operating Lease Term and Discount Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>40805 - Disclosure - LEASES - Rental Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureLeasesRentalExpenseDetails</Role>
      <ShortName>LEASES - Rental Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>40901 - Disclosure - GOODWILL AND INTANGIBLE ASSETS - Changes in Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssetsChangesInGoodwillDetails</Role>
      <ShortName>GOODWILL AND INTANGIBLE ASSETS - Changes in Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>40902 - Disclosure - GOODWILL AND INTANGIBLE ASSETS - Changes in Core Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssetsChangesInCoreDepositsDetails</Role>
      <ShortName>GOODWILL AND INTANGIBLE ASSETS - Changes in Core Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>40903 - Disclosure - GOODWILL AND INTANGIBLE ASSETS - Estimated Annual Amortization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssetsEstimatedAnnualAmortizationDetails</Role>
      <ShortName>GOODWILL AND INTANGIBLE ASSETS - Estimated Annual Amortization (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>40904 - Disclosure - GOODWILL AND INTANGIBLE ASSETS - Core Deposit Intangible (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureGoodwillAndIntangibleAssetsCoreDepositIntangibleDetails</Role>
      <ShortName>GOODWILL AND INTANGIBLE ASSETS - Core Deposit Intangible (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>41001 - Disclosure - INTEREST RECEIVABLE AND OTHER ASSETS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInterestReceivableAndOtherAssetsDetails</Role>
      <ShortName>INTEREST RECEIVABLE AND OTHER ASSETS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureInterestReceivableAndOtherAssetsTables</ParentRole>
      <Position>78</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>41101 - Disclosure - DEPOSITS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureDepositsDetails</Role>
      <ShortName>DEPOSITS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureDepositsTables</ParentRole>
      <Position>79</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>41201 - Disclosure - BORROWINGS - Federal Home Loan Bank (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBorrowingsFederalHomeLoanBankDetails</Role>
      <ShortName>BORROWINGS - Federal Home Loan Bank (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>41202 - Disclosure - BORROWINGS - Federal Funds Line - Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBorrowingsFederalFundsLineCommitmentsDetails</Role>
      <ShortName>BORROWINGS - Federal Funds Line - Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>41203 - Disclosure - BORROWINGS - Federal Funds Line - Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBorrowingsFederalFundsLineOutstandingDetails</Role>
      <ShortName>BORROWINGS - Federal Funds Line - Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>41204 - Disclosure - BORROWINGS - Junior Subordinated Deferrable Interest Debentures (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBorrowingsJuniorSubordinatedDeferrableInterestDebenturesDetails</Role>
      <ShortName>BORROWINGS - Junior Subordinated Deferrable Interest Debentures (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>41205 - Disclosure - BORROWINGS - Subordinated Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureBorrowingsSubordinatedNotesDetails</Role>
      <ShortName>BORROWINGS - Subordinated Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>41301 - Disclosure - INTEREST PAYABLE AND OTHER LIABILITIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureInterestPayableAndOtherLiabilitiesDetails</Role>
      <ShortName>INTEREST PAYABLE AND OTHER LIABILITIES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureInterestPayableAndOtherLiabilitiesTables</ParentRole>
      <Position>85</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>41401 - Disclosure - OTHER EXPENSES - Tabular Disclosure (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureOtherExpensesTabularDisclosureDetails</Role>
      <ShortName>OTHER EXPENSES - Tabular Disclosure (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>41402 - Disclosure - OTHER EXPENSES - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureOtherExpensesAdditionalInformationDetails</Role>
      <ShortName>OTHER EXPENSES - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>41501 - Disclosure - EQUITY INCENTIVE PLANS - General Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlansGeneralInformationDetails</Role>
      <ShortName>EQUITY INCENTIVE PLANS - General Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>41502 - Disclosure - EQUITY INCENTIVE PLANS - Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlansCompensationExpenseDetails</Role>
      <ShortName>EQUITY INCENTIVE PLANS - Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>41503 - Disclosure - EQUITY INCENTIVE PLANS - Unrecognized Compensation Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlansUnrecognizedCompensationCostDetails</Role>
      <ShortName>EQUITY INCENTIVE PLANS - Unrecognized Compensation Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>41504 - Disclosure - EQUITY INCENTIVE PLANS - Restricted Stock Grant Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureEquityIncentivePlansRestrictedStockGrantActivityDetails</Role>
      <ShortName>EQUITY INCENTIVE PLANS - Restricted Stock Grant Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>41601 - Disclosure - FAIR VALUE MEASUREMENT - Recurring (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueMeasurementRecurringDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENT - Recurring (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>41602 - Disclosure - FAIR VALUE MEASUREMENT - Nonrecurring (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueMeasurementNonrecurringDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENT - Nonrecurring (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>41701 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureFairValueOfFinancialInstrumentsDetails</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.unitedbusinessbank.com/role/DisclosureFairValueOfFinancialInstrumentsTables</ParentRole>
      <Position>94</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>41801 - Disclosure - COMMITMENTS AND CONTINGENCIES - Off-balance Sheet Liabilities - Tabular Disclosure (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingenciesOffBalanceSheetLiabilitiesTabularDisclosureDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Off-balance Sheet Liabilities - Tabular Disclosure (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>41802 - Disclosure - COMMITMENTS AND CONTINGENCIES - Off-balance Sheet Liabilities - Reserve (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingenciesOffBalanceSheetLiabilitiesReserveDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Off-balance Sheet Liabilities - Reserve (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>41803 - Disclosure - COMMITMENTS AND CONTINGENCIES - Other Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingenciesOtherAssetsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Other Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>41804 - Disclosure - COMMITMENTS AND CONTINGENCIES - Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingenciesDepositsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="bcml-20210930x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>41805 - Disclosure - COMMITMENTS AND CONTINGENCIES - Local Agency Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.unitedbusinessbank.com/role/DisclosureCommitmentsAndContingenciesLocalAgencyDepositsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Local Agency Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="bcml-20210930x10q.htm">bcml-20210930x10q.htm</File>
    <File>bcml-20210930.xsd</File>
    <File>bcml-20210930_cal.xml</File>
    <File>bcml-20210930_def.xml</File>
    <File>bcml-20210930_lab.xml</File>
    <File>bcml-20210930_pre.xml</File>
    <File>bcml-20210930ex3115ccef2.htm</File>
    <File>bcml-20210930ex312ae7821.htm</File>
    <File>bcml-20210930xex32.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/stpr/2021</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2021</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
