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Financial Instruments [Domain] U.S. Government-sponsored Mortgage-backed and Related Securities [Member] Debt securities collateralized by real estate mortgage loans (mortgages), issued by US Government Sponsored Enterprises. Cash dividends declared (in dollars per share) Common Stock, Dividends, Per Share, Declared (in dollars per share) Investments in Affordable Housing Tax Credits Projects [Text Block] The entire disclosure for investments in affordable housing tax credit projects. Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Preferred stock (no par value, 350,000 shares authorized, none outstanding) us-gaap_Liabilities Total liabilities cbkm_HeldToMaturityQualitativeDisclosureNumberOfPositions Held-to-maturity, Qualitative Disclosure, Number of Positions Number of investment positions in held-to-maturity investments. 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Federal funds sold represent the excess federal funds held by one commercial bank which it lends to another commercial bank, usually at an agreed-upon (federal funds) rate of interest. Such loans are made for legal reserve requirement purposes of the borrowing bank and generally are of short-duration (overnight). It also includes the interest income from aggregate of all domestic and foreign interest-bearing deposit. Retained Earnings [Member] Professional and director fees A fee charged for services from professionals such as doctors, lawyers, accountants. And also includes director fees. Debit card processing expenses Expenses incurred for debit card processing services. Real Estate [Member] Financial Instrument Performance Status [Domain] Premises and equipment, net Financial Asset, Aging [Axis] Financial Instrument Performance Status [Axis] Recorded investment Total loans Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss Financing Receivable, Nonaccrual [Table Text Block] Financial Asset, Aging [Domain] us-gaap_ProvisionForLoanLossesExpensed Provision for credit losses on loans us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss Held-to-maturity, amortized cost Held-to-maturity Securities, Amortized Cost Basis Financial Asset, 30 to 59 Days Past Due [Member] us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss Available-for-sale securities, amortized cost Total securities available-for-sale us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest Less allowance for credit losses Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Balance Balance Financial Asset, 60 to 89 Days Past Due [Member] Financial Asset, Equal to or Greater than 90 Days Past Due [Member] us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear Loans, Year Five us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear Loans, Prior us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear Loans, Year Three us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear Loans, Year Four us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear Loans, Year One Fair Value Disclosures [Text Block] us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear Loans, Year Two Fair Value, by Balance Sheet Grouping [Table Text Block] Supplemental disclosure of cash flow information: us-gaap_FinancingReceivableExcludingAccruedInterestRevolving Loans, Revolving us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan Loans, Revolving Converted to Term us-gaap_ShorttermDebtFairValue Short-term borrowings us-gaap_LoansHeldForSaleFairValueDisclosure Loans held for sale Redemption of equity security Federal income taxes Collateral Held [Domain] Collateral Held [Axis] us-gaap_PaymentsToAcquireLifeInsurancePolicies Purchase of bank owned life insurance Other Commitments [Table] Accumulated other comprehensive loss Accumulated other comprehensive income (loss), net Accumulated other comprehensive income (loss), net Common stock, par value (in dollars per share) FDIC assessments Amount of expense (income) for Federal Deposit Insurance Corporation (FDIC) insurance. 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Segment Reporting, Policy [Policy Text Block] us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross Restricted stock expense Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Premises and equipment purchases Issuance of stock-based incentive plan shares Collateral Pledged [Member] us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan Issuance of shares associated with dividend reinvestment plan and stock purchase plan us-gaap_NoninterestExpense Total noninterest expenses Noninterest expenses Financial Asset, Not Past Due [Member] us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures Restricted stock expense us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture (in shares) us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan Stock Issued During Period, Shares, Dividend Reinvestment Plan (in shares) Accumulated other comprehensive income (loss), tax Accumulated other comprehensive income (loss), tax us-gaap_AociTaxAttributableToParent us-gaap_AociBeforeTaxAttributableToParent Accumulated other comprehensive income (loss), before tax Accumulated other comprehensive income (loss), before tax Other Pledged Collateral [Member] Represents the other assets pledged as collateral. us-gaap_TreasuryStockValue Treasury stock, at cost (48,639 common shares as of March 31, 2026 and June 30, 2025) Cash flows from operating activities Cash flow from investing activities Net cash from operating activities Cash flow from financing activities us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used in investing activities Residential Real Estate and Consumer Segments [Member] Represents residential real estate and consumer segments. us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash from financing activities us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt Purchases of securities, available-for-sale Sale of securities, available-for-sale us-gaap_AssetsFairValueDisclosure Assets, Fair Value Disclosure Net affordable housing tax credit investment Amount of investment in qualified affordable housing projects, net of amortization. Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Net increase in deposit accounts Accounting Policies [Abstract] Schedule of Investments in Affordable Housing Projects [Table Text Block] Tabular disclosure of investments in affordable housing projects. Farmland [Member] Represents farmland. Accrued interest receivable and other assets Mortgage-Backed Security, Issued by US Government-Sponsored Enterprise [Member] Land Development [Member] Represents land development. US Treasury Securities [Member] US States and Political Subdivisions Debt Securities [Member] us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss Net loans us-gaap_PaymentsForProceedsFromLoansAndLeases Net increase in loans Income Statement [Abstract] Commercial, Commercial Real Estate, Farmland and Land Development Segment [Member] Represents Commercial, Commercial Real Estate, Farmland and Land Development Segment. Securities, available-for-sale us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest Available-for-sale securities, fair value Total securities available-for-sale us-gaap_NumberOfOperatingSegments Number of Operating Segments Securities, held-to-maturity (fair value of $4,556 at March 31, 2026 and $5,026 at June 30, 2025) Treasury stock, shares (in shares) Treasury Stock, Common [Member] Net income Net income Net income us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic Net income available to common shareholders Financial Asset, Past Due [Member] Mortgage banking activity Provision for credit losses on unfunded commitments Amount of provision for unfunded commitments expensed. us-gaap_ForeclosedAssets Repossessed Assets Amortization of intangible us-gaap_InterestIncomeExpenseNet Net interest income cbkm_AccruedInterestReceivableFairValueDisclosure Accrued interest receivable Fair value portion of accrued interest receivable. Accumulated Other Comprehensive Income (Loss) [Table] Restricted Stock [Member] Nonaccrual, Interest Income Accounting Standards Update and Change in Accounting Principle [Table] Occupancy and equipment us-gaap_OtherNoninterestExpense Other Bank owned life insurance income us-gaap_NoninterestIncome Total noninterest income Noninterest income Measurement Basis [Axis] Fair Value Hierarchy and NAV [Domain] Demand and Savings Deposits [Member] Represents the information pertaining to demand and savings deposits. Other us-gaap_NoninterestIncomeOther Transfer from loans to repossessed assets Measurement Frequency [Domain] Time Deposits [Member] Represents the information pertaining to time deposits. Statement of Financial Position [Abstract] Provision for expected credit losses us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal Marketing and advertising us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery Recoveries us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff Charge-offs Loans, Total, Write-offs Fair Value, Nonrecurring [Member] Fair Value, Recurring [Member] dei_DocumentType Document Type Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount Document Information [Line Items] Document Quarterly Report Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis Document Information [Table] us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive Securities [Axis] us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment Dilutive effect of restricted stock (in shares) dei_EntityInteractiveDataCurrent Entity Interactive Data Current Document Transition Report us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Total common shares and dilutive potential common shares (in shares) us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate Available-for-sale Securities, Debt Maturities, Single Maturity Date us-gaap_WeightedAverageNumberOfSharesOutstandingBasic Weighted average common shares outstanding (in shares) Basic and diluted earnings per share (in dollars per share) Basic income per share (in dollars per share) Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing us-gaap_FinancingReceivableExcludingAccruedInterest90DaysOrMorePastDueStillAccruing Nonaccrual, No Allowance Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table] Nonaccrual Financing Receivable, Excluding Accrued Interest, Nonaccrual us-gaap_Deposits Total deposits Noninterest-bearing demand Core deposit intangible, net Document Fiscal Period Focus Document Fiscal Year Focus Savings Amendment Flag Common Stock [Member] Securities losses, net us-gaap_FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount Financing Receivable, Unamortized Loan Cost (Fee) and Purchase Premium (Discount) Goodwill dei_DocumentPeriodEndDate Document Period End Date Other equity securities, at cost us-gaap_PaymentsForProceedsFromFederalReserveBankStock Net change in Federal Home Loan Bank stock, at cost Interest and dividend income Residential Portfolio Segment [Member] Legal Entity [Axis] us-gaap_InterestAndDividendIncomeOperating Total interest and dividend income Consumer Portfolio Segment [Member] Commercial Real Estate Portfolio Segment [Member] Financing Receivable, Allowance for Credit Loss [Table] dei_EntityFileNumber Entity File Number us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax Net unrealized (losses) gains Entity Tax Identification Number Non-cash items: us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss Entity [Domain] Entity Central Index Key dei_EntityRegistrantName Entity Registrant Name Doubtful [Member] Performing Financial Instruments [Member] dei_EntityCurrentReportingStatus Entity Current Reporting Status Special Mention [Member] us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss Gross realized losses Substandard [Member] Entity Incorporation, State or Country Code Interest bearing demand Pass [Member] Current Fiscal Year End Date us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 Net current period other comprehensive loss, tax Entity Filer Category dei_EntityShellCompany Entity Shell Company us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax Income tax effect Entity Emerging Growth Company Nonperforming Financial Instruments [Member] Entity Small Business Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Interest expense us-gaap_InterestBearingDepositsInBanks Federal funds sold and interest-bearing deposits in financial institutions cbkm_PolicyTable Equity securities Deposits Entity Address, State or Province Entity Address, City or Town Retained earnings us-gaap_InterestExpenseOperating Total interest expense Entity Address, Address Line One dei_CityAreaCode City Area Code Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis dei_LocalPhoneNumber Local Phone Number Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis Entity Address, Postal Zip Code Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis Class of Stock [Axis] us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm Federal Home Loan Bank advances Class of Financing Receivable [Axis] Class of Financing Receivable [Domain] dei_EntityCommonStockSharesOutstanding Entity Common Stock, Shares Outstanding (in shares) Earnings Per Share [Text Block] Preferred stock, par value (in dollars per share) cbkm_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAccumulatedAmortization Less: amortization Amount of accumulated amortization expense for investment that generates income tax credit and other income tax benefit under tax credit program. us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax Unrealized holding losses on available-for-sale securities arising during the period, tax Unrealized (losses) gains arising during the period Gross loans us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossFeeAndLoanInProcess Schedule of Other Investments in Affordable Housing Projects [Table Text Block] Tabular disclosure of the other investments in affordable housing projects. Internal Credit Assessment [Axis] Unrealized holding losses on available-for-sale securities arising during the period, net Short-term borrowings us-gaap_InterestExpenseShortTermBorrowings Other Debt Obligations [Member] us-gaap_HeldToMaturitySecuritiesFairValue Debt Securities, Held-to-Maturity, Fair Value Held-to-maturity Securities, Fair Value us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss Net interest income after provision for credit losses Issuance of treasury stock for vested restricted stock awards The fair value of treasury stock issued for stock awards. Investments Classified by Contractual Maturity Date [Table Text Block] Internal Credit Assessment [Domain] Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Fair Value Securities, taxable Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value Securities, tax-exempt Basis of Accounting, Policy [Policy Text Block] Amounts reclassified from accumulated other comprehensive income, tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Cash on hand and noninterest-bearing deposits in financial institutions us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax Reclassification adjustment for net losses included in income us-gaap_CashCashEquivalentsAndFederalFundsSold Total cash and cash equivalents us-gaap_Assets Total assets us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax Amounts reclassified from accumulated other comprehensive income, net cbkm_PercentOfAvailableForSaleDebtSecuritiesPortfolio Percent of Available for Sale Debt Securities Portfolio The percent of available for sale debt securities portfolio. Non-rated [Member] Related to non-rated securities. Rated [Member] Related to rated securities. us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod Financing Receivable, Excluding Accrued Interest, Modified in Period, Amount us-gaap_EarningsPerShareDiluted Dilutive income per share (in dollars per share) cbkm_QualitativeDisclosureNumberOfPositions Available-for-sale, Qualitative Disclosure, Number of Positions Number of securities in the Company's portfolio. us-gaap_OtherRealEstate Other Real Estate External Credit Rating, Standard & Poor's [Domain] Accounts and Financing Receivables [Table] cbkm_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerFairValue Obligations of state and political subdivisions Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer. Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] cbkm_DebtSecuritiesHeldtomaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLosses Obligations of state and political subdivisions Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer. cbkm_DebtSecuritiesHeldtomaturityUnrealizedLossPositionAccumulatedLosses Obligations of state and political subdivisions Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position. Fair Value by Liability Class [Domain] cbkm_DebtSecuritiesHeldtomaturityUnrealizedLossPositionsFairValue Obligations of state and political subdivisions Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position. Interest Cash surrender value of life insurance us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff Loans, Prior, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff Loans, Loans, Revolving, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff Loans, Year Four, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff Loans, Year Five, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff Loans, Year Two, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff Loans, Year Three, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff Loans, Year One, Write-offs us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff Loans, Revolving Converted to Term, Write-offs Third Party Residential Mortgage Warehouse Line of Credit [Member] Represents a third party residential mortgage warehouse line of credit. cbkm_FinancingReceivableExcludingAccruedInterestNetOfAmortizedCosts Financing Receivable, Excluding Accrued Interest, Net of Amortized Costs Represents the amount of financing receivable excluding accrued interest offset by amortized costs. us-gaap_StockholdersEquity Total shareholders’ equity Balance Balance Commercial and Industrial [Member] Represents commercial and industrial. us-gaap_PaymentsOfDividendsCommonStock Dividends paid us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings Repayments of Federal Home Loan Bank advances ecd_Rule10b51ArrTrmntdFlag Rule 10b5-1 Arrangement Terminated [Flag] Noninterest income (in scope of Topic 606) ecd_Rule10b51ArrAdoptedFlag Rule 10b5-1 Arrangement Adopted [Flag] Commitments and contingent liabilities Marketable Securities [Table Text Block]