Document And Entity Information Due after ten years, fair value Note To Financial Statement Details Textual Note 2 - Revenue Recognition Note 3 - Stock-based Compensation Due in one year or less, amortized costs Note 4 - Earnings Per Share Note 5 - Fair Value Measurements Due in one year or less, fair value Note 6 - Accumulated Other Comprehensive Income Due after one year through five years, fair value Note 7 - Investment and Equity Securities Due after five years through ten years, fair value Note 8 - Loans and Related Allowance for Loan and Lease Losses Note 9 - Lease Commitments us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax Net of tax Note 2 - Revenue Recognition - Disaggregation of Revenue (Details) Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Note 3 - Stock-based Compensation - Stock Option Activity (Details) Note 3 - Stock-based Compensation - Activity Related to Restricted Stock Units Awarded (Details) Note 4 - Earnings Per Share - Shares Used in Calculation of Earnings Per Share (Details) Note 5 - Fair Value Measurements - Assets Measured on a Recurring Basis (Details) us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax Amount reclassified from accumulated other comprehensive income Note 5 - Fair Value Measurements - Assets Measured on a Nonrecurring Basis (Details) Note 5 - Fair Value Measurements - Additional Quantitative Information About Assets Measured at Fair Value on Non-recurring Basis (Details) Note 5 - Fair Value Measurements - Estimated Fair Value of the Company's Financial Instruments (Details) Note 6 - Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax (Details) us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax Income taxes Note 6 - Accumulated Other Comprehensive Income - Significant Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive Income (Loss) (Details) Note 7 - Investment and Equity Securities - Amortized Cost and Fair Values of Securities Available for Sale (Details) Note 7 - Investment and Equity Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) Note 7 - Investment and Equity Securities - Sales of Available for Sale Securities (Details) Note 7 - Investment and Equity Securities - Gross Unrealized Losses and Fair Value (Details) US States and Political Subdivisions Debt Securities [Member] Note 8 - Loans and Related Allowance for Loan and Lease Losses - Major Classifications of Net Loans (Details) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Primary Segments of the Loan Portfolio (Details) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Allowance for Loan Losses (Details) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Impaired Loans by Class (Details) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Additional Information on Impaired Loans (Details) us-gaap_OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Total Note 8 - Loans and Related Allowance for Loan and Lease Losses - Classes of the Loan Portfolio Summarized by Credit Quality (Details) Share-based Payment Arrangement, Option, Activity [Table Text Block] Note 8 - Loans and Related Allowance for Loan and Lease Losses - Past Due Loans (Details) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Nonaccrual Loans (Details) Proceeds from dividend reinvestment and purchase plan Proceeds from dividend reinvestment & purchase plan. Pass [Member] Granted, weighted average grant date fair value per share (in dollars per share) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Troubled Debt Restructurings (Details) Note 8 - Loans and Related Allowance for Loan and Lease Losses - Troubled Debt Restructurings Subsequently Defaulted (Details) Vested, weighted average grant date fair value per share (in dollars per share) Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Note 9 - Lease Commitments - Leases Costs (Details) Note 9 - Lease Commitments - Weighted Average Remaining Lease Term and Discount Rate Information (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue Nonvested, weighted average grant date fair value per share (in dollars per share) Nonvested, weighted average grant date fair value per share (in dollars per share) Note 9 - Lease Commitments - Maturities of Lease liabilities (Details) Noncash investing transactions: Notes To Financial Statements us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance Nonvested (in shares) Nonvested (in shares) Notes To Financial Statements [Abstract] us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent Other comprehensive loss before reclassification US Government Agencies Debt Securities [Member] Internal Credit Assessment [Axis] Proceeds from repayments and maturities Internal Credit Assessment [Domain] Granted (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested (in shares) us-gaap_OtherComprehensiveIncomeLossNetOfTax Total other comprehensive income (loss) mbcn_NumberOfDaysPastDue Number of Days Past Due The number of days past due. Equity Securities [Member] Exercisable, weighted average exercise price (in dollars per share) Loans held for sale Proceeds from the sale of other real estate owned Exercisable (in shares) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares, Ending Balance Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance Outstanding, weighted average exercise price (in dollars per share) Outstanding, weighted average exercise price (in dollars per share) Change in accounting principle for adoption of ASU 2016-01 Change in accounting principle, ASC 2016-01 Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from measurement and recognition of financial instruments that are marked to fair value and reported as available-for-sale. us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans Exercised, weighted average exercise price (in dollars per share) Subsequently Defaulted [Member] Represents information pertaining to troubled debt restructurings that subsequently defaulted. ATM Banking Fees [Member] Information pertaining to ATM banking fees. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance Outstanding (in shares) Outstanding (in shares) Overdraft Fees [Member] Information pertaining to overdraft fees. mbcn_RevenueFromInterestIncomeAndNoninterestIncomePercent Revenue from Interest Income and Noninterest Income, Percent Represents the percentage of revenue from interest income and noninterest income. Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Service Charge and Other Fees [Member] Information pertaining to service charge and other fees. mbcn_PercentageOfPortfolio Available-for-sale Securities, Percentage of Portfolio Represents a percentage of the available-for-sale securities portfolio. us-gaap_PolicyTextBlockAbstract Accounting Policies Investment securities gains on sale, net Investment securities gains on sale, net Special Mention [Member] Substandard [Member] Doubtful [Member] us-gaap_TransferOfInvestments Transfer of equity securities from investment securities available for sale, at fair value Impaired loans, discount rate Impaired loans, discount rate Value of input used to measure impaired loans. Appraisal of Collateral [Member] Information pertaining to appraisal of collateral. us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Purchase of premises and equipment us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements Additional common stock equivalents (stock options and restricted stock) used to calculate diluted earnings per share (in shares) Transfers from loans to other real estate owned us-gaap_WeightedAverageNumberOfSharesTreasuryStock Average treasury stock shares (in shares) us-gaap_FinancingReceivableModificationsRecordedInvestment Financing Receivable, Troubled Debt Restructuring Gain on equity securities (Loss) gain on equity securities Equity Securities, FV-NI, Unrealized Gain (Loss), Total Gain on equity securities Outside Consultant [Member] Represents information relating to an outside consultant. us-gaap_WeightedAverageNumberOfSharesIssuedBasic Weighted-average common shares issued (in shares) Threshold For Loans Evaluated For Impairment [Member] The threshold for loans evaluated for impairment. Commercial And Industrial [Member] Represents information by loans categorized as commercial and industrial. Criticized Relationships [Member] Loans with credit ratings of Special Mention, Substandard, or Doubtful. LIABILITIES Real Estate Mortgage Portfolio Segment [Member] Portfolio segment of the company's total financing receivables related to real estate mortgage receivables. Real Estate Construction Porfolio Segment [Member] Portfolio segment of the company's total financing receivables related to real estate construction receivables. Number of contracts, subsequently defaulted us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1 Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts Residential Loan [Member] Loan to finance the purchase of residential real estate, including but not limited to, land or building. Pre-modification outstanding recorded investment us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 Post-modification outstanding recorded investment us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 Commercial Loans [Member] Loan relating to commercial purchases. us-gaap_Assets TOTAL ASSETS Cash paid during the year for: Recorded investment, subsequently defaulted us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1 Schedule Of Financing Receivable By Segment [Table Text Block] The tabular disclosure for financing receivables, by segment. us-gaap_ShorttermDebtFairValue Short-term borrowings Number of contracts us-gaap_FinancingReceivableModificationsNumberOfContracts2 Compensation and Employee Benefit Plans [Text Block] Loan Restructuring Modification [Axis] us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Loan Restructuring Modification [Domain] Extended Maturity [Member] Impaired Financing Receivables [Table Text Block] Schedule of Additional Information Related to Impaired Loans [Table Text Block] Schedule of additional information related to impaired loans. Financing Receivable, Troubled Debt Restructuring [Table Text Block] Other Restructurings [Member] Other restructurings. Award Type [Domain] Award Type [Axis] Net income NET INCOME Core deposit intangibles us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing Loans, 90+ days past due and accruing Financing Receivable Credit Quality Indicators [Table Text Block] Restricted Stock [Member] us-gaap_FinancingReceivableRecordedInvestmentCurrent Loans, current balance us-gaap_FinancingReceivableRecordedInvestmentPastDue Loans, past due mbcn_RestrictStockCash Restricted stock cash portion Represents the cash portion of restrict stock. us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus Loans, nonacrrual status Noncash financing transactions: Noncash operating transactions: Financial Asset, 30 to 59 Days Past Due [Member] Antidilutive Securities [Axis] Employee Stock Option and Restricted Stock [Member] Information pertaining to employee stock option and restricted stock. Finance lease liabilities added to borrowed funds Represents the non-cash financing transactions of finance lease liabilities added to borrowed funds. Financial Asset, 60 to 89 Days Past Due [Member] Antidilutive Securities, Name [Domain] mbcn_FinanceLeaseAssetsAddedToPremisesAndEquipmentNoncashInvestingTransactions Finance lease assets added to premises and equipment Represents the noncash investment transaction of finance lease assets added to premises and equipment. Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Financing Receivable, Past Due [Table Text Block] Operating lease liabilities added to other, net Represents the non-cash operating transaction for net operating lease liabilities added to other. Financial Asset, Period Past Due [Axis] mbcn_OperatingLeaseAssetsAddedToOtherNetNoncashOperatingTransaction Operating lease assets added to other, net Represents operating lease assets added to other, net for non-cash operating transaction. Financial Asset, Period Past Due [Domain] Premises and equipment, net Goodwill us-gaap_PaymentsForProceedsFromLoansAndLeases Increase in loans, net us-gaap_NotesReceivableGross Financing Receivable, before Allowance for Credit Loss, Total us-gaap_PaymentsToAcquireFederalHomeLoanBankStock Purchase of restricted stock Subordinated Debt Securities [Member] Represents information about subordinated debt securities. Expected to vest (in shares) The amount of share-based compensation arrangement by share-based payment award, equity instruments other than options that are expected to vest. INVESTING ACTIVITIES Expected to vest, weighted average grant date fair value per share (in dollars per share) The weighted average fair value as of the grant date pertaining to an equity-based award plan other than a stock (or unit) option plan that is expected to vest. Investment securities available for sale, at fair value Fair Value us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet Other, net EARNINGS PER SHARE Earnings Per Share [Text Block] Equity securities, at fair value Increase in accrued interest payable mbcn_ImpairedLoansFairValue Impaired loans, fair value estimate Fair value portion of impaired loans. us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments Income before income taxes Income taxes us-gaap_IncomeTaxExpenseBenefit us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held, Ending Balance Premises and Equipment, Net [Member] Primary financial statement caption encompassing premises and equipment. Tax effect Accrued Interest Receivable and Other Assets [Member] Primary financial statement caption encompassing accrued interest receivable and other assets. Lease Disclosure [Text Block] The entire disclosure for operating, finance, sale leaseback leases. mbcn_LeaseRightofuseAssetNet Lease, Right-of-Use Asset, Net Amount of lessee's right to use underlying asset under operating and finance lease. Interest Payable and Other Liabilities [Member] Primary financial statement caption encompassing interest payable and other liabilities. us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax Tax effect Other Borrowings [Member] Primary financial statement caption encompassing other borrowing. mbcn_LesseeOperatingLeaseRemainingTerm Lessee, Operating Lease, Remaining Term Remaining term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. mbcn_NumberOfBranchLocationsByUtilizedLeases Number of Branch Locations by Utilized Leases Represents number of branch locations by utilized locations. Operating and Finance Lease, Liability, Maturity [Table Text Block] Tabular disclosure of undiscounted cash flows of operating and finance lease liability. Includes, but is not limited to, reconciliation of undiscounted cash flows to operating and finance lease liability recognized in statement of financial position. Lease, Term and Discount Rate [Table Text Block] Tabular disclosure of term and discount rate of lease. Other Amount of other cost from finance lease. us-gaap_CashAndCashEquivalentsAtCarryingValue CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD CASH AND CASH EQUIVALENTS AT END OF PERIOD Salaries and employee benefits Provision Fluctuation [Member] Represents information related to provision fluctuation. Cash and due from banks us-gaap_AllocatedShareBasedCompensationExpense Share-based Payment Arrangement, Expense us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment Individually evaluated for impairment us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment Collectively evaluated for impairment Individually evaluated for impairment Collectively evaluated for impairment Amendment Flag us-gaap_ComprehensiveIncomeNetOfTax Comprehensive income Treasury acquired, shares (in shares) Treasury Stock, Shares, Acquired Common stock, shares outstanding (in shares) Balance (in shares) Balance (in shares) us-gaap_GainsLossesOnSalesOfOtherRealEstate Net gain on other real estate owned Gain on sale of loans Gain on sale of loans Current Fiscal Year End Date us-gaap_AllowanceForLoanAndLeaseLossesAdjustmentsNet Allowance for Loan and Lease Losses, Adjustments, Other us-gaap_DebtInstrumentInterestRateStatedPercentage Impaired loans, fair value estimate us-gaap_LeaseCost Total lease cost Recoveries Weighted-average discount rate), Operating Lease Document Fiscal Period Focus Operating lease cost Document Fiscal Year Focus us-gaap_EquitySecuritiesFvNiRealizedGainLoss Equity Securities, FV-NI, Realized Gain (Loss), Total us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs Allowance for Loan and Lease Losses, Write-offs Charge-offs Lease, Cost [Table Text Block] Document Period End Date Weighted-average term (years), Operating Lease (Year) Entity Emerging Growth Company Document Type Entity Small Business Entity Shell Company us-gaap_DividendsCommonStockCash Cash dividends Document Information [Line Items] Document Information [Table] Entity Filer Category Entity Current Reporting Status us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet Decrease (increase) in accrued interest receivable Software amortization expense Bank-owned life insurance Statement of Comprehensive Income [Abstract] Entity Central Index Key Entity Registrant Name Entity [Domain] Legal Entity [Axis] Amortization of core deposit intangibles Core deposit intangible amortization us-gaap_TreasuryStockValueAcquiredCostMethod Treasury shares acquired (17,747) us-gaap_TreasuryStockValue Treasury stock, at cost; 403,912 and 386,165 shares Entity Common Stock, Shares Outstanding (in shares) Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Net loans Net loans Advertising expense Taxable Municipal Bonds [Member] Nontaxable Municipal Bonds [Member] us-gaap_LoansAndLeasesReceivableDeferredIncome Loans and Leases Receivable, Deferred Income, Total Professional fees Loans Total loans Dividend reinvestment and purchase plan Less allowance for loan and lease losses Loans and Leases Receivable, Allowance, Ending Balance Less: Allowance for loan and lease losses ALLL balance, period start ALLL balance, period end Dividend reinvestment and purchase plan (in shares) Investments [Domain] Trading Symbol us-gaap_LoansAndLeasesReceivableBeforeFeesGross Loans and Leases Receivable, before Fees, Gross Data processing costs Occupancy expense Investment Type [Axis] Stock options exercised (in shares) us-gaap_TableTextBlock Notes Tables us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale Origination of loans held for sale Stock options exercised Proceeds from sale of loans us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation Stock-based compensation, net (in shares) Stock-based compensation, net us-gaap_LiabilitiesAndStockholdersEquity TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY Reported Value Measurement [Member] us-gaap_CashCashEquivalentsAndFederalFundsSold Cash and cash equivalents Federal funds sold Retained earnings Accumulated other comprehensive income (loss) Measurement Input, Discount Rate [Member] us-gaap_InterestExpenseOther Other borrowings us-gaap_InterestExpense Total interest expense us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements us-gaap_OperatingLeaseLiability Operating Lease, Liability, Total us-gaap_InterestExpenseShortTermBorrowings Short-term borrowings us-gaap_OperatingLeaseRightOfUseAsset Operating Lease, Right-of-Use Asset us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue Total undiscounted cash flows us-gaap_FinanceLeaseLiability Finance Lease, Liability, Total us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount Impact of present value discount Deferred income tax us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree 2021 Measurement Input Type [Axis] us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour 2022 Measurement Input Type [Domain] us-gaap_FinanceLeaseRightOfUseAsset Finance Lease, Right-of-Use Asset us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive 2023 us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive 2024 and thereafter Deposits us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo 2020 Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] us-gaap_StockOptionPlanExpense Stock-based compensation expense us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear 2019 INTEREST EXPENSE Depreciation and amortization of premises and equipment, net mbcn_GainLossOnSalesOfLoansExcludingStudentLoansNet Gain on sale of loans The net gain (loss) resulting from a sale of loans (excluding student loans), including adjustments to record loans classified as held-for-sale at the lower-of-cost-or-market and fair value adjustments to loan held for investment purposes mbcn_EstimatedSellingCostsOfImpairedLoans Estimated Selling Costs of Impaired Loans The estimated amount of selling costs that would incur when impaired loans sold. Dividends on stock us-gaap_InterestAndDividendIncomeOperating Total interest and dividend income us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments Amortization of premium and discount on investment securities, net mbcn_BankOwnedLifeInsuranceFairValue Bank-owned life insurance The fair value portion of a life insurance policy on an officer, executive or employee for which the reporting entity (a bank) is entitled to proceeds from the policy upon death of the insured or surrender of the insurance policy. Interest-earning deposits in other institutions mbcn_InterestReceivableFairValue Accrued interest receivable The fair value portion as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable. mbcn_AccruedInterestPayableFairValueDisclosure Accrued interest payable Fair value portion of accrued interest payable. us-gaap_InterestIncomeFederalFundsSold Federal funds sold us-gaap_OtherLiabilitiesFairValueDisclosure Other borrowings Change in accounting principle for adoption of ASU 2018-02 Change in accounting principle, ASC 2018-02 us-gaap_LoansHeldForSaleFairValueDisclosure Loans held for sale Investment securities: us-gaap_CashAndCashEquivalentsFairValueDisclosure Cash and cash equivalents Taxable interest Tax-exempt interest Treasury stock, shares (in shares) Treasury Stock, Shares, Ending Balance Fair Value, Nonrecurring [Member] Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Common stock, no par value; 10,000,000 shares authorized, 3,646,497 and 3,630,497 shares issued; 3,242,585 and 3,244,332 shares outstanding Adjustments to reconcile net income to net cash provided by operating activities: us-gaap_AmortizationOfDeferredLoanOriginationFeesNet Accretion of deferred loan fees, net Measurement Frequency [Axis] Measurement Frequency [Domain] Interest and fees on loans Fair Value, Recurring [Member] Common stock, shares authorized (in shares) Common stock, shares issued (in shares) Common stock, par value (in dollars per share) Statistical Measurement [Domain] Maximum [Member] Minimum [Member] Weighted Average [Member] Product and Service [Axis] Product and Service [Domain] Statistical Measurement [Axis] INTEREST AND DIVIDEND INCOME Interest on deposits and borrowings Income taxes Portion at Fair Value Measurement [Member] [Default] Estimate of Fair Value Measurement [Member] Total noninterest income Noninterest income revenue Measurement Basis [Axis] Fair Value, Inputs, Level 3 [Member] Fair Value Hierarchy and NAV [Domain] Earnings on bank-owned life insurance Earnings on bank-owned life insurance Earnings on bank-owned life insurance Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] NONINTEREST INCOME Fair Value Hierarchy and NAV [Axis] Provision Provision for loan losses us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss NET INTEREST INCOME AFTER PROVISION FOR LOAN LOSSES us-gaap_InterestIncomeExpenseNet NET INTEREST INCOME OPERATING ACTIVITIES Statement [Line Items] AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Accrued interest receivable and other assets AOCI Attributable to Parent [Member] STOCKHOLDERS' EQUITY us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure Federal Home Loan Bank stock Financial liabilities: us-gaap_LoansReceivableFairValueDisclosure Net loans Deposit Account [Member] Financial assets: Fair Value Disclosures [Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] ASSETS us-gaap_Liabilities TOTAL LIABILITIES us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash provided by financing activities us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash provided by operating activities us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used in investing activities us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease Increase in cash and cash equivalents Accounting Standards Update 2016-02 [Member] Type of Adoption [Domain] Related allowance Adjustments for New Accounting Pronouncements [Axis] Interest income recognized mbcn_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisesInPeriodForStockAndCash Exercised (in shares) Number of share options (or share units) exercised during the current period for atock and cash. Recorded investment, with no related allowance us-gaap_PaymentsOfDividendsCommonStock Cash dividends Recorded investment, with related allowance Impaired loans Recorded investment Average recorded investment Unpaid principal balance, with no related allowance Unpaid principal balance, with related allowance Unpaid principal balance Other expense us-gaap_NoninterestExpense Total noninterest expense us-gaap_PaymentsForRepurchaseOfCommonStock Repurchase of treasury shares Scenario [Domain] Equipment expense Forecast [Member] Federal deposit insurance expense Retained Earnings [Member] us-gaap_ProceedsFromStockOptionsExercised Stock options exercised Treasury Stock [Member] Scenario [Axis] NONINTEREST EXPENSE Common Stock [Member] Other borrowings Equity Components [Axis] Equity Component [Domain] Class of Financing Receivable [Domain] Class of Financing Receivable [Axis] Financing Receivable Portfolio Segment [Domain] Consumer Portfolio Segment [Member] Financing Receivable Portfolio Segment [Axis] Comprehensive Income (Loss) Note [Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] us-gaap_RepaymentsOfOtherDebt Repayment of other borrowings Disaggregation of Revenue [Table Text Block] Revenue from Contract with Customer [Text Block] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Accounting Policies [Abstract] Significant Accounting Policies [Text Block] us-gaap_ShortTermBorrowings Total short-term borrowings Cash dividends per share (in dollars per share) Federal Home Loan Bank advances Debt Securities [Member] Title of 12(b) Security Short-term borrowings: us-gaap_DepositsFairValueDisclosure Deposits Legal Entity of Counterparty, Type [Axis] Legal Entity Type of Counterparty [Domain] Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Increase (decrease) in short-term borrowings, net Accrued interest payable and other liabilities us-gaap_PaymentsToAcquireAvailableForSaleSecurities Purchases Proceeds from sale of securities Proceeds from sales us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Weighted-average common shares and common stock equivalents used to calculate diluted earnings per share (in shares) Statement [Table] Statement of Financial Position [Abstract] Diluted (in dollars per share) us-gaap_WeightedAverageNumberOfSharesOutstandingBasic Weighted-average common shares and common stock equivalents used to calculate basic earnings per share (in shares) Basic (in dollars per share) Assets measured on a recurring basis Statement of Cash Flows [Abstract] Statement of Stockholders' Equity [Abstract] Other comprehensive income (loss) Total other comprehensive income (loss) Income Statement [Abstract] us-gaap_AvailableForSaleSecuritiesGrossRealizedGains Gross realized gains Financing Receivable, Nonaccrual [Table Text Block] Financing Receivable, Current, Allowance for Credit Loss [Table Text Block] Federal funds purchased Interest Expense us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss Total, Gross Unrealized Losses us-gaap_Deposits Total deposits us-gaap_FinanceLeaseLiabilityPaymentsDue Total undiscounted cash flows us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss Less than Twelve Months, Gross Unrealized Losses Financing lease amortization expense Amortization of right-of-use asset us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss Twelve Months or Greater, Gross Unrealized Losses Investments Classified by Contractual Maturity Date [Table Text Block] us-gaap_FinanceLeaseLiabilityPaymentsDueYearFive 2023 Interest-bearing demand us-gaap_FinanceLeaseLiabilityPaymentsDueAfterYearFive 2024 and thereafter us-gaap_FinanceLeaseLiabilityUndiscountedExcessAmount Impact of present value discount Schedule of Unrealized Loss on Investments [Table Text Block] us-gaap_FinanceLeaseLiabilityPaymentsDueYearTwo 2020 Net increase in deposits us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses Gross realized losses us-gaap_FinanceLeaseLiabilityPaymentsDueYearThree 2021 Noninterest-bearing demand Realized Gain (Loss) on Investments [Table Text Block] us-gaap_FinanceLeaseLiabilityPaymentsDueYearFour 2022 Time Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Unrealized gains on available-for-sale securities Less than Twelve Months, Fair Value Money market Twelve Months or Greater, Fair Value Total, Fair Value Weighted-average discount rate, Fiance Lease us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax Reclassification adjustment for investment securities gains included in net income us-gaap_FinanceLeaseLiabilityPaymentsRemainderOfFiscalYear 2019 Savings Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block] Fair Value, Assets Measured on Recurring Basis [Table Text Block] Net unrealized holding gain (loss) on available-for-sale investment securities Weighted-average term (years), Fiance Lease (Year) FINANCING ACTIVITIES us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue Security Owned and Pledged as Collateral, Fair Value, Total us-gaap_StockholdersEquity TOTAL STOCKHOLDERS' EQUITY Balance Balance Ohio state franchise tax Ohio state franchise tax. Class of Stock [Axis] us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax Gross unrealized losses Gross unrealized losses Gross unrealized gains Gross unrealized gains Schedule of Weighted Average Number of Shares [Table Text Block] Financial Service, Other [Member] us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit Amortized cost Amortized costs Amortized cost Due after one year through five years, amortized costs Due after five years through ten years, amortized costs Due after ten years, amortized costs us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit