<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>153</ContextCount>
  <ElementCount>286</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>45</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>5</UnitCount>
  <MyReports>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>995200090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>995200100 - Statement - CONDENSED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/StatementCondensedBalanceSheets</Role>
      <ShortName>CONDENSED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>995200200 - Statement - CONDENSED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/StatementCondensedStatementsOfIncome</Role>
      <ShortName>CONDENSED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>995200300 - Statement - CONDENSED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/StatementCondensedStatementsOfComprehensiveIncome</Role>
      <ShortName>CONDENSED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>995200400 - Statement - CONDENSED STATEMENTS OF EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/StatementCondensedStatementsOfEquity</Role>
      <ShortName>CONDENSED STATEMENTS OF EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>995200500 - Statement - CONDENSED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/StatementCondensedStatementsOfCashFlows</Role>
      <ShortName>CONDENSED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>995210101 - Disclosure - Nature of Operations and Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureNatureOfOperationsAndSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Nature of Operations and Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>995210201 - Disclosure - INVESTMENT SECURITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecurities</Role>
      <ShortName>INVESTMENT SECURITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>995210301 - Disclosure - LOANS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoans</Role>
      <ShortName>LOANS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>995210401 - Disclosure - DEPOSITS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureDeposits</Role>
      <ShortName>DEPOSITS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>995210501 - Disclosure - OTHER BORROWINGS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureOtherBorrowings</Role>
      <ShortName>OTHER BORROWINGS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>995210601 - Disclosure - FAIR VALUE MEASUREMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>FAIR VALUE MEASUREMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>995210701 - Disclosure - INCOME TAXES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>INCOME TAXES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>995210801 - Disclosure - EMPLOYEE BENEFITS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureEmployeeBenefits</Role>
      <ShortName>EMPLOYEE BENEFITS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>995210901 - Disclosure - RETAINED EARNINGS AND REGULATORY CAPITAL</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureRetainedEarningsAndRegulatoryCapital</Role>
      <ShortName>RETAINED EARNINGS AND REGULATORY CAPITAL</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>995211001 - Disclosure - COMMITMENTS AND UNCERTAINTIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureCommitmentsAndUncertainties</Role>
      <ShortName>COMMITMENTS AND UNCERTAINTIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>995211101 - Disclosure - SUBSEQUENT EVENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>SUBSEQUENT EVENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>99920102 - Disclosure - Nature of Operations and Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureNatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Nature of Operations and Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureNatureOfOperationsAndSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>99930203 - Disclosure - INVESTMENT SECURITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecuritiesTables</Role>
      <ShortName>INVESTMENT SECURITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureInvestmentSecurities</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>99930303 - Disclosure - LOANS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansTables</Role>
      <ShortName>LOANS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureLoans</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>99930403 - Disclosure - DEPOSITS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureDepositsTables</Role>
      <ShortName>DEPOSITS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureDeposits</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>99930503 - Disclosure - OTHER BORROWINGS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureOtherBorrowingsTables</Role>
      <ShortName>OTHER BORROWINGS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureOtherBorrowings</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>99930603 - Disclosure - FAIR VALUE MEASUREMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>FAIR VALUE MEASUREMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>99930703 - Disclosure - INCOME TAXES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>INCOME TAXES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>99940101 - Disclosure - Nature of Operations and Summary of Significant Accounting Policies - Concentrations of credit risk (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureNatureOfOperationsAndSummaryOfSignificantAccountingPoliciesConcentrationsOfCreditRiskDetails</Role>
      <ShortName>Nature of Operations and Summary of Significant Accounting Policies - Concentrations of credit risk (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>99940102 - Disclosure - Nature of Operations and Summary of Significant Accounting Policies - Income taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureNatureOfOperationsAndSummaryOfSignificantAccountingPoliciesIncomeTaxesDetails</Role>
      <ShortName>Nature of Operations and Summary of Significant Accounting Policies - Income taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureNatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPolicies</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>99940201 - Disclosure - INVESTMENT SECURITIES - Amortized cost and fair value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecuritiesAmortizedCostAndFairValueDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Amortized cost and fair value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>99940202 - Disclosure - INVESTMENT SECURITIES - Contractual maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecuritiesContractualMaturityDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Contractual maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>99940203 - Disclosure - INVESTMENT SECURITIES - Continuous loss position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecuritiesContinuousLossPositionDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Continuous loss position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>99940204 - Disclosure - INVESTMENT SECURITIES - Number and aggregate depreciation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecuritiesNumberAndAggregateDepreciationDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Number and aggregate depreciation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>99940205 - Disclosure - INVESTMENT SECURITIES - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureInvestmentSecuritiesAdditionalInformationDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>99940301 - Disclosure - LOANS - Major Classification (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansMajorClassificationDetails</Role>
      <ShortName>LOANS - Major Classification (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>99940302 - Disclosure - LOANS - Narration (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansNarrationDetails</Role>
      <ShortName>LOANS - Narration (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>99940303 - Disclosure - LOANS - Allowance for credit losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansAllowanceForCreditLossesDetails</Role>
      <ShortName>LOANS - Allowance for credit losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>99940304 - Disclosure - LOANS - Unfunded Loan Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansUnfundedLoanCommitmentsDetails</Role>
      <ShortName>LOANS - Unfunded Loan Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>99940305 - Disclosure - LOANS - Provision for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansProvisionForCreditLossesDetails</Role>
      <ShortName>LOANS - Provision for Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>99940306 - Disclosure - LOANS - Grading category and year (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansGradingCategoryAndYearDetails</Role>
      <ShortName>LOANS - Grading category and year (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>99940307 - Disclosure - LOANS - Loan portfolio aging analysis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansLoanPortfolioAgingAnalysisDetails</Role>
      <ShortName>LOANS - Loan portfolio aging analysis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>99940308 - Disclosure - LOANS - Nonaccrual loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureLoansNonaccrualLoansDetails</Role>
      <ShortName>LOANS - Nonaccrual loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>99940401 - Disclosure - DEPOSITS - Contractual Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureDepositsContractualMaturitiesDetails</Role>
      <ShortName>DEPOSITS - Contractual Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>99940402 - Disclosure - DEPOSITS - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureDepositsNarrativeDetails</Role>
      <ShortName>DEPOSITS - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>99940501 - Disclosure - OTHER BORROWINGS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureOtherBorrowingsDetails</Role>
      <ShortName>OTHER BORROWINGS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureOtherBorrowingsTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>99940502 - Disclosure - OTHER BORROWINGS - Contractual maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureOtherBorrowingsContractualMaturitiesDetails</Role>
      <ShortName>OTHER BORROWINGS - Contractual maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>99940601 - Disclosure - FAIR VALUE MEASUREMENTS - Assets measured at fair value on a recurring basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureFairValueMeasurementsAssetsMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - Assets measured at fair value on a recurring basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>99940602 - Disclosure - FAIR VALUE MEASUREMENTS - carrying value and estimated fair value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureFairValueMeasurementsCarryingValueAndEstimatedFairValueDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - carrying value and estimated fair value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>99940701 - Disclosure - INCOME TAXES - Income tax provision (benefit) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxesIncomeTaxProvisionBenefitDetails</Role>
      <ShortName>INCOME TAXES - Income tax provision (benefit) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>99940702 - Disclosure - INCOME TAXES - Effective Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxesEffectiveTaxRateReconciliationDetails</Role>
      <ShortName>INCOME TAXES - Effective Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>99940703 - Disclosure - INCOME TAXES - Income taxes paid, net of refunds (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxesIncomeTaxesPaidNetOfRefundsDetails</Role>
      <ShortName>INCOME TAXES - Income taxes paid, net of refunds (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>99940704 - Disclosure - INCOME TAXES - Net deferred tax asset (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxesNetDeferredTaxAssetDetails</Role>
      <ShortName>INCOME TAXES - Net deferred tax asset (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>99940705 - Disclosure - INCOME TAXES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureIncomeTaxesDetails</Role>
      <ShortName>INCOME TAXES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureIncomeTaxesTables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>99940801 - Disclosure - EMPLOYEE BENEFITS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureEmployeeBenefitsDetails</Role>
      <ShortName>EMPLOYEE BENEFITS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureEmployeeBenefits</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>99940901 - Disclosure - RETAINED EARNINGS AND REGULATORY CAPITAL (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureRetainedEarningsAndRegulatoryCapitalDetails</Role>
      <ShortName>RETAINED EARNINGS AND REGULATORY CAPITAL (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureRetainedEarningsAndRegulatoryCapital</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>99941001 - Disclosure - COMMITMENTS AND UNCERTAINTIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureCommitmentsAndUncertaintiesDetails</Role>
      <ShortName>COMMITMENTS AND UNCERTAINTIES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureCommitmentsAndUncertainties</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="tmb-20260331x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>99941101 - Disclosure - SUBSEQUENT EVENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://bankwith-csb.com/role/DisclosureSubsequentEventsDetails</Role>
      <ShortName>SUBSEQUENT EVENTS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://bankwith-csb.com/role/DisclosureSubsequentEvents</ParentRole>
      <Position>56</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>tmb-20260331.xsd</File>
    <File>tmb-20260331_cal.xml</File>
    <File>tmb-20260331_def.xml</File>
    <File>tmb-20260331_lab.xml</File>
    <File>tmb-20260331_pre.xml</File>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="tmb-20260331x10q.htm">tmb-20260331x10q.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="775">http://fasb.org/us-gaap/2026</BaseTaxonomy>
    <BaseTaxonomy items="27">http://xbrl.sec.gov/dei/2026</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2026</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
