Document And Entity Information Marketable Securities, Policy [Policy Text Block] Statistical Measurement [Axis] Note To Financial Statement Details Textual us-gaap_DividendsPayableDateDeclaredDayMonthAndYear Dividends Payable, Date Declared Significant Accounting Policies Note 1 - Significant Accounting Policies Federal income tax expense Federal income tax expense ecd_NonRule10b51ArrTrmntdFlag Non-Rule 10b5-1 Arrangement Terminated [Flag] Note 2 - Securities ecd_NonRule10b51ArrAdoptedFlag Non-Rule 10b5-1 Arrangement Adopted [Flag] Note 3 - Loans and Allowance for Credit Losses Trading Arrangements, by Individual [Table] Note 4 - Premises and Equipment, Net Material Terms of Trading Arrangement [Text Block] Note 5 - Deposits Note 6 - Securities Sold Under Agreements to Repurchase Financial Instrument [Axis] Note 7 - Other Borrowings Investment in Debt and Equity Securities and Other Trading Assets [Text Block] Note 8 - Stock-based Compensation Money market, percentage Note 9 - Commitments and Off-balance-sheet Risk Minimum [Member] Note 10 - Derivatives and Hedging Activities us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax Securities available for sale, gross unrealized losses Interest-bearing checking, percentage Note 11 - Fair Values of Financial Instruments Securities available for sale, gross unrealized gains Statistical Measurement [Domain] Note 12 - Fair Values One to Four Family Mortgages [Member] Segment of the company's total financing receivables related to 1-4 family mortgages. Maximum [Member] Note 13 - Business Combinations Note 14 - Regulatory Matters Note 15 - Business Segment Information Business Combination, Share Price (in dollars per share) Note 1 - Significant Accounting Policies - Noninterest Income (Details) Note 2 - Securities - Available-for-sale Securities (Details) us-gaap_FiniteLivedIntangibleAssetsPurchaseAccountingAdjustments Intangible Asset, Finite-Lived, Measurement Period Adjustment Note 2 - Securities - Securities in a Continuous Loss Position (Details) Grades 5-7 [Member] A credit rating between 5 and 7. Note 2 - Securities - Debt Securities by Maturity (Details) Grades 1-4 [Member] A credit rating between 1 and 4. Period increase (decrease) The percentage of increase or (decrease) during the period in loans and leases receivable net of deferred income. Savings, percentage Note 3 - Loans and Allowance for Credit Losses - Components of Loan Portfolio (Details) Grades 8-9 [Member] A credit rating between 8 and 9. Time Deposits, percentage Note 3 - Loans and Allowance for Credit Losses - Age Analysis of Past Due Loans (Details) Financial Asset, 30 to 89 Days Past Due [Member] Financial asset more than 29 days past due but fewer than 90 days past due. Note 3 - Loans and Allowance for Credit Losses - Nonaccrual Loans (Details) Financing Receivable, Modified, Financial Effect [Table Text Block] Tabular disclosure of the financial effect of financing receivable modified for debtor experiencing financial difficulty. Recoveries Note 3 - Loans and Allowance for Credit Losses - Loan Vintage (Details) Note 3 - Loans and Allowance for Credit Losses - Activity in Allowance for Loan Losses and the Recorded Investments in Loans (Details) Financing Receivable, Modified, Amortized Cost [Table Text Block] Tabular disclosure of amortized cost of financing receivable modified for debtor experiencing financial difficulty. Note 3 - Loans and Allowance for Credit Losses - Financial Effect by Type of Modification (Details) Total deposits, percent increase (decrease) Aggregate Increase (Decrease) in Percentage of Deposits The percentage of increase or (decrease) during the period in deposit liabilities. Note 3 - Loans and Allowance for Credit Losses - Amortized Cost of Modified Loans (Details) Note 4 - Premises and Equipment, Net - Summary of Premises and Equipment (Details) Note 4 - Premises and Equipment, Net - Future Lease Payments (Details) Note 5 - Deposits - Summary of Deposits (Details) Note 6 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) Note 7 - Other Borrowings - Maturities of Currently Outstanding FHLB Advances (Details) us-gaap_DebtSecuritiesAvailableForSaleRestricted Debt Securities, Available-for-Sale, Restricted Note 7 - Other Borrowings - Maturities of Currently Outstanding FHLBI Amortizing Advances (Details) Note 8 - Stock-based Compensation - Summary of Restricted Stock Activity (Details) Note 8 - Stock-based Compensation - Shares Grant to Board Directors (Details) Note 9 - Commitments and Off-balance-sheet Risk - Exposure to Credit Losses (Details) Note 10 - Derivatives and Hedging Activities - Fair Value of Derivative Instruments (Details) Subordinated notes Note 10 - Derivatives and Hedging Activities - The Netting Arrangement of Derivative Instruments (Details) Debt Securities, Available-for-Sale [Table] Note 11 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) Note 12 - Fair Values - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) Summary of Deposits and Percentage Change in Deposits [Table Text Block] Tabular disclosure of deposits and the percentage change in deposits. Note 12 - Fair Values - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) Note 13 - Business Combinations - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) Note 13 - Business Combinations - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) (Parentheticals) mbwm_AggregateLocalDepositLiabilities Total local deposits Value of liabilities related to local deposits. Note 13 - Business Combinations - Business Combination, Pro Forma Information (Details) Out-of-area time, $100,000 and over The aggregate amount of out-of-area time deposits (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more. Note 14 - Regulatory Matters - Actual Capital Levels and Minimum Levels (Details) Note 15 - Business Segment Information - Reconciliation of Assets from Segment to Consolidated (Details) Noninterest-bearing demand, percentage Percentage of money in noninterest-bearing domestic accounts that entitle the depositor to withdraw funds at any time without prior notice, also known as demand deposits. Notes To Financial Statements Salaries and benefits Notes To Financial Statements [Abstract] us-gaap_DividendsCommonStockCash Cash dividends Performance Shares [Member] mbwm_AggregatePercentageOfLocalDeposits Total local deposits, percentage Represents a percentage of domestic deposit liabilities. Out-of-area time, $100,000 and over, percentage The percentage of out-of-area time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more. mbwm_AggregatePercentageOfDeposits Total deposits, percentage Represents a percentage of total deposits. Noninterest-bearing demand, percent increase (decrease) Percentage of increase or (decrease) in noninterest-bearing domestic accounts that entitle the depositor to withdraw funds at any time without prior notice, also known as demand deposits. Financial Instruments [Domain] Money market, percent increase (decrease) Percentage of increase or (decrease) in interest-bearing domestic money market demand account deposit liabilities. Interest-bearing checking, percent increase (decrease) Percentage of increase or (decrease) in interest-bearing domestic checking deposit liabilities. us-gaap_CommonStockDividendsPerShareDeclared Common Stock, Dividends, Per Share, Declared (in dollars per share) Savings, percent increase (decrease) Percentage of increase or (decrease) in interest-bearing domestic savings deposit liabilities. Saving deposits bear interest and have no stated maturity. Total local deposits The percentage of increase or (decrease) during the period in domestic deposit liabilities. Securities Sold under Agreements to Repurchase [Member] Out-of-area time, $100,000 and over, percent increase (decrease) Percentage of increase or (decrease) in out-of-area time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more. Weighted Average [Member] us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet Accrued interest receivable Dividends [Axis] Debt Security Category [Axis] Dividends [Domain] Segment Reporting [Text Block] Securities available for sale, continuous unrealized loss position, 12 months or more Securities available for sale, continuous unrealized loss position, less than 12 months Award Type [Axis] Segment Reporting [Table Text Block] Adjustments to reconcile net income to net cash from operating activities Preferred stock, no par value; 1,000,000 shares authorized; none issued Plan Name [Axis] Banking Regulation, Regulatory Capital Requirement, Compliance [Table] us-gaap_Liabilities Total liabilities Plan Name [Domain] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Total Cost Share-Based Payment Arrangement, Expense Consolidation Items [Axis] us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and shareholders’ equity Title and Position [Axis] Segment Reporting [Table] us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets Other assets Stock-based compensation expense us-gaap_ShareBasedCompensation Subsequent Event [Member] Consolidation Items [Domain] LIABILITIES AND SHAREHOLDERS' EQUITY Federal Home Loan Bank of Indianapolis [Member] Share-Based Payment Arrangement [Text Block] Maturities of Currently Outstanding FHLB Advances [Table Text Block] Tabular disclosure of the maturities of currently outstanding Federal Home Loan Bank advances. Summary of Contractual Amounts of Financial Instruments With Off Balance Sheet Risk [Table Text Block] Tabular disclosure of contractual amounts of financial instruments with off-balance sheet risk. Net change in: Preferred stock, issued (in shares) Consumer Other Financing Receivable 1 [Member] Class of financing receivables related to other consumer financing receivables. Preferred stock, authorized (in shares) Shares Granted (in shares) Portion at Fair Value Measurement [Member] Reported Value Measurement [Member] Fair Value, by Balance Sheet Grouping [Table] mbwm_AccruedInterestReceivableFairValueDisclosure Accrued interest receivable Fair value disclosure for interest which has been accrued but unpaid. Dividend reinvestment plan us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net change in cash and cash equivalents Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Product and Service, Revenue [Table Text Block] Furniture and equipment depreciation, rent and maintenance us-gaap_CashAndCashEquivalentsFairValueDisclosure Cash and cash equivalents Estimate of Fair Value Measurement [Member] Cash dividends per common share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid (in dollars per share) us-gaap_ServicingAssetAtFairValueAmount Servicing Asset at Fair Value, Amount Common equity tier 1, ratio Total capital to be well capitalized, ratio Other Consumer Loans [Member] Represents the other consumer loans. Total capital, ratio us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period us-gaap_ServicingAssetAtAmortizedValue Servicing Asset at Amortized Cost US Government Agencies Debt Securities [Member] Total capital minimum required for capital adequacy, ratio Capital Required for Capital Adequacy to Risk Weighted Assets Tier 1 capital to average assets, ratio Tier 1 capital minimum required for capital adequacy, ratio Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Tier 1 capital to average assets minimum required for capital adequacy, ratio Statement [Table] Tier 1 capital to average assets to be well capitalized, ratio Credit Facility [Axis] Credit Facility [Domain] Tier 1 capital to be well capitalized, ratio Tier 1 capital, ratio Securities available for sale, continuous unrealized loss position, unrealized loss Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] us-gaap_LoansReceivableFairValueDisclosure Loans, net us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 Debt Instrument, Basis Spread on Variable Rate Securities available for sale, continuous unrealized loss position Debt Securities, Available-for-Sale, Unrealized Loss Position us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity Line of Credit Facility, Maximum Borrowing Capacity Derivative Liabilities Interest rate swaps Interest rate swaps us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure FHLBI stock us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Financing Receivable, Allowance for Credit Loss [Table Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Nonvested, beginning (in shares) Nonvested, end (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue Nonvested, weighted average fair value, beginning (in dollars per share) Nonvested, weighted average fair value, end (in dollars per share) us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity Line of Credit Facility, Remaining Borrowing Capacity Grants (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) srt_StockRepurchaseProgramAuthorizedAmount1 Stock Repurchase Program, Authorized Amount Financing Receivable, Past Due [Table Text Block] Grants, weighted average fair value (in dollars per share) Average daily balance during the period us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure Securities sold under agreements to repurchase Long-Term Debt, Type [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Forfeited (in shares) us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure FHLBI advances Maximum daily balance during the period Stock grants to directors for retainer fees Stock grants to directors for retainer fees (in shares) Product and Service [Domain] Product and Service [Axis] mbwm_TrustPreferredSecuritiesIncludedInTierOneCapital Trust Preferred Securities Included in Tier One Capital Trust preferred securities held by the trust that are included in Tier One Capital and subject to certain limitations. Consolidated Entities [Axis] Vested, weighted average fair value (in dollars per share) Consolidated Entities [Domain] mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent Maximum Restricted Core Element Allowed in Tier One Capital Percent The maximum amount of restricted core elements allowed in tier one capital expressed as a percent. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested (in shares) us-gaap_ContinuingInvolvementWithTransferredFinancialAssetsPrincipalAmountOutstanding Continuing Involvement with Transferred Financial Assets, Principal Amount Outstanding us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive Thereafter Time Deposits, percent increase (decrease) Percentage of increase or (decrease) in domestic time deposits (including certificates of deposits, individual retirement accounts and open accounts). Recent Events [Policy Text Block] Accounting policy disclosing the recent events the company has had. mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOneCapital Maximum Level of Consolidated Aggregate Assets Allowing for Inclusion of Trust Preferred Securities in Tier One Capital The maximum level of consolidated aggregate assets allowing for inclusion of trust preferred securities in Tier 1 Capital under the Dodd-Frank Act. us-gaap_RepaymentsOfDebt Payments on term note us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue Total undiscounted lease payments Core conversion costs The amount of core conversion costs. mbwm_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities Deferred Tax Liabilities, Measurement Period Adjustment Amount of increase (decrease) from measurement period adjustment of liability representing future economic benefit arising from other liability acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized. mbwm_PreferredSecuritiesOfSubsidiaryTrust Preferred Securities of Subsidiary Trust Trust preferred securities possesses characteristics of both equity and debt issues and are generally issued by bank holding companies. Available-for-Sale Securities [Member] us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent Operating Lease, Weighted Average Discount Rate, Percent Loan Origination Commitments [Member] Proceeds from sales of mortgage loans held for sale Related allowance Allowance of nonaccrual financing receivable. Commercial Real Estate [Member] With related allowance recorded, principal balance Amortized cost of financing receivable on nonaccrual status with allowance for credit loss. Excludes net investment in lease. us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths 2026 Financial instruments, derivative liability us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive 2030 Loans, including fees us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) Financial instruments, derivative assets us-gaap_OperatingLeaseExpense Operating Lease, Expense Financing Receivable by Origination Year [Table Text Block] Tabular disclosure of financing receivable by origination year. Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree 2028 ASSETS mbwm_MortgageLoansHeldForSale Mortgage loans held for sale Carrying value of mortgage loans that are held with the intention to sell or be securitized in the near future. Measurement Frequency [Axis] us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo 2027 Statement [Line Items] us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour 2029 Fair Value Hierarchy and NAV [Axis] Common stock, issued (in shares) Common stock, outstanding (in shares) Award Type [Domain] Amortizing Advances [Member] Represents the amortizing advances. Common stock, authorized (in shares) Bullet Advances [member] Represents the bullet advances. Proceeds from Federal Home Loan Bank advances Financing Receivable, Term Loan Amortized cost of financing receivable term loan. Mortgage Banking Activity [Policy Text Block] us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1 Stock Repurchase Program, Remaining Authorized Repurchase Amount Accrued interest and other liabilities us-gaap_AccruedLiabilitiesCurrentAndNoncurrent Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Percent of portfolio Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Common stock, no par value; 40,000,000 shares authorized; 17,285,911 shares issued and outstanding at June 30, 2026, and 17,181,096 shares issued and outstanding at December 31, 2025 Common equity tier 1 capital minimum required for capital adequacy, ratio Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy to Risk Weighted Assets The minimum common equity tier one capital ratio (common equity tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. Common equity tier 1 capital to be well capitalized, ratio Common equity tier 1 capital ratio (common equity tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action. Business Combination, Recognized Asset Acquired and Liability Assumed [Table Text Block] Short-Term Debt, Type [Domain] us-gaap_PolicyTextBlockAbstract Accounting Policies us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements us-gaap_TableTextBlock Notes Tables O 2026 Q2 Dividends [Member] O 2026 Q2 Dividends Short-Term Debt, Type [Axis] Proceeds from bank owned life insurance claims us-gaap_ComprehensiveIncomeNetOfTax Comprehensive income (loss) Average interest rate at end of period Subordinated Debentures [Member] Represents subordinated debentures. Subordinated Notes [Member] Represents subordinated notes. Subsequent Events [Text Block] mbwm_AccretionOfAcquiredLoans Accretion of acquired loans Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations. mbwm_SubordinatedDebtPrincipalAmount Subordinated Debt, Principal Amount Principal amount of subordinated debt. Commitments Contingencies and Guarantees [Text Block] mbwm_SubordinatedBorrowingRedemptionPricePercentageOfPrincipalAmount Subordinated Borrowing, Redemption Price, Percentage of Principal Amount Redemption price as a percentage of principal amount. Credit Card Lines of Credit [Member] Relating to credit card lines of credit. us-gaap_FinancingReceivableUnamortizedLoanFeeCost Financing Receivable, Unamortized Loan Cost (Fee) Fair Value Measurement and Measurement Inputs, Recurring and Nonrecurring [Text Block] Significant Accounting Policies [Text Block] Federal Home Loan Bank advances Long-Term Federal Home Loan Bank Advances Proceeds from maturities, calls and repayments of securities available for sale us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount Less effect of discounting Present value of future lease payments (lease liability) us-gaap_OperatingLeaseLiability Operating Lease, Liability Thereafter us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueAfterFiveYearsOfBalanceSheetDate us-gaap_DepositsFairValueDisclosure Deposits 2026 us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate 2029 us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromThreeToFourYearsOfBalanceSheetDate Acquisition costs 2028 us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate 2030 us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromFourToFiveYearsOfBalanceSheetDate Total, amortized cost us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis Debt Securities, Available-for-Sale, Amortized Cost 2027 us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations Subordinated debt Federal Home Loan Bank, Advance, Branch of FHLBank [Table] Standby Letters of Credit [Member] Term note Statement of Stockholders' Equity [Abstract] Intangible Asset, Finite-Lived, Class [Axis] Extended Maturity [Member] Payroll Processing [Member] Represents payroll processing. Principal Forgiveness [Member] Customer Service [Member] Represents customer service. Loan Restructuring Modification [Axis] Statement of Comprehensive Income [Abstract] Intangible Asset, Finite-Lived, Class [Domain] Loan Restructuring Modification [Domain] Contractual Interest Rate Reduction [Member] Statement of Cash Flows [Abstract] Financing Receivable Portfolio Segment [Axis] Interest Rate Swap Liabilities [Member] Relating to interest rate swap liabilities. Financing receivable, term loan write offs Amount of writeoff of term loan financing receivables. mbwm_FinancingReceivableAllowanceForCreditLossPeriodIncreaseDecreaseFromForecastChanges Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease) From Forecast Changes Amount of increase (decrease) in allowance for credit loss on financing receivable due economic forecast changes. us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent Other comprehensive income (loss), net of tax Long-Term Debt, Type [Domain] Shareholders' equity Core Deposits [Member] Equity Components [Axis] Financing Receivable Portfolio Segment [Domain] Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block] Equity Component [Domain] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] AOCI Attributable to Parent [Member] Fair Value, Inputs, Level 1 [Member] Retained Earnings [Member] us-gaap_SubordinatedBorrowingInterestRate Subordinated Borrowing, Interest Rate mbwm_FairValueInputsDiscountFactor Fair Value Inputs, Discount Factor Discount factor used to further reduce the balance sheet carrying amount of property or other assets. Subordinated Borrowing, Name [Domain] Residential Real Estate [Member] Financial Instrument Performance Status [Domain] Premises and equipment, net Premises and equipment, net Financial Asset, Aging [Axis] Property, plant and equipment, gross mbwm_SharebasedCompensationArrangementBySharebasedPaymentAwardMinimumEmployeePayrollDeduction Share-Based Compensation Arrangement by Share-Based Payment Award, Minimum Employee Payroll Deduction Minimum Employee Payroll Deduction Financial Instrument Performance Status [Axis] Subordinated Borrowing [Axis] Subsequent Event Type [Domain] Financing Receivable, Nonaccrual [Table Text Block] Subsequent Event [Table] Subsequent Event Type [Axis] Financial Asset, Aging [Domain] us-gaap_ProvisionForLoanLossesExpensed Financing Receivable, Credit Loss, Expense (Reversal) Provision for credit losses Provision for credit losses Corporate and Bank Board Members [Member] Related to corporate and bank board members. mbwm_ProceedsInjectedIncreaseToEquityCapitalFromIssuanceOfSubordinatedLongtermDebt Proceeds Injected, Increase to Equity Capital From Issuance of Subordinated Long-term Debt The amount of proceeds that being injected and increase to equity capital from the issuance of subordinated long-term debt. Financial Asset, 30 to 59 Days Past Due [Member] Furniture and Fixtures [Member] us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue Stock-based compensation expense Financial Asset, 60 to 89 Days Past Due [Member] Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Gain Contingencies [Table] Interest Rate Swap Assets [Member] Relating to interest rate swap assets. Fair Value Disclosures [Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Supplemental disclosures of cash flows information us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] mbwm_NumberOfUnconsolidatedBusinessTrustsFormedToIssueTrustPreferredSecurities Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities The number of unconsolidated business trusts formed to issue trust preferred securities. Secured Overnight Financing Rate (SOFR) [Member] mbwm_PolicyTable us-gaap_MortgagesHeldForSaleFairValueDisclosure Loan, Mortgage, Held-for-Sale, Fair Value Disclosure Mercantile Plans [Member] Compensation plans that originated with Mercantile. Real Estate Dependent Loans and Foreclosed Assets [Member] Information pertaining to both real estate dependent loans and foreclosed assets. O 2026 Q3 Dividends [Member] Related to dividends. Collateral Held [Domain] Collateral Held [Axis] Mortgage banking income Information By Category Of Debt Security [Domain] Subordinated debentures us-gaap_PaymentsToAcquireFederalReserveStock Purchases of Federal Reserve Bank stock Tier 1 capital minimum required for capital adequacy, amount us-gaap_GainLossOnSaleOfPropertyPlantEquipment Net loss from sales and disposals of premises and equipment us-gaap_PaymentsToAcquireLifeInsurancePolicies Purchases of bank owned life insurance Tier 1 capital to be well capitalized, amount us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Less: accumulated depreciation Tier 1 capital, amount Common stock, par value (in dollars per share) Accumulated other comprehensive income (loss) Tier 1 capital to average assets, minimum required for capital adequacy, amount Tier 1 capital to average assets to be well capitalized, amount Tier 1 capital to average assets, amount Term Note [Member] Represents Term Note. mbwm_CapitalConservationBuffer Capital Conservation Buffer An additional amount held in risk-based capital designed to ensure that banks build up capital buffers outside periods of stress which can be drawn down as losses are incurred. The requirement is based on simple capital conservation rules designed to avoid breaches of minimum capital requirements. Mercantile Bank [Member] Represents the legal entity, Mercantile Bank. mbwm_BusinessCombinationRecognizedAssetAcquiredLoansNet Loans, net Amount of loans net acquired in business combination and recognized at acquisition date. mbwm_BusinessCombinationRecognizedAssetAcquiredAvailableForSaleSecurities Securities available for sale Amount of available for sale securities acquired in business combination and recognized at acquisition date. us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest Income before federal income tax expense mbwm_BusinessCombinationRecognizedLiabilityAssumedDepositsLiability Deposits Amount of deposits liability assumed in business combination and recognized at acquisition date. mbwm_BusinessCombinationRecognizedAssetAcquiredOtherAsset Other assets Amount of asset acquired in business combination and recognized at acquisition date, classified as other including current and noncurrent. Data processing costs Eastern Michigan Financial Corp. [Member] Represents Eastern Michigan Financial Corp.. mbwm_BusinessCombinationRecognizedAssetAcquiredInterestEarningDeposits Interest-earning deposits Amount of interest earning deposits acquired in business combination and recognized at acquisition date. mbwm_BusinessCombinationRecognizedAssetAcquiredCashAndDueFromBanks Cash and due from banks Amount of cash and due from banks acquired in business combination and recognized at acquisition date. Provision for credit losses mbwm_BusinessCombinationProFormaInformationProFormaProvisionForCreditLosses Amount of pro forma provision for credit losses of combined entity as if acquisition date of business combination occurred as of beginning of period. Income before income taxes mbwm_BusinessCombinationProFormaInformationProFormaIncomeLossBeforeIncomeTax Amount, before tax, of pro forma income (loss) of combined entity as if acquisition date of business combination occurred as of beginning of period. Debt Disclosure [Text Block] Income tax expense mbwm_BusinessCombinationProFormaInformationProFormaIncomeTaxExpense Amount of pro forma income tax expense of combined entity as if acquisition date of business combination occurred as of beginning of period. Net interest income mbwm_BusinessCombinationProFormaInformationProFormaNetInterestIncome Amount of pro forma net interest income of combined entity as if acquisition date of business combination occurred as of beginning of period. mbwm_BusinessCombinationRecognizedLiabilityAssumedOtherLiability Other liabilities Amount of liability assumed in business combination and recognized at acquisition date, classified as other, including current and noncurrent. All Other States and Their Political Subdivisions [Member] States and their political subdivisions other than the State of Michigan and its political subdivision. Other Debt and Equity Securities [Member] Investments in debt and equity securities classified as other. Noninterest expense mbwm_BusinessCombinationProFormaInformationProFormaNoninterestExpense Amount of pro forma noninterest expense of combined entity as if acquisition date of business combination occurred as of beginning of period. State of Michigan and All Its Political Subdivisions [Member] Securities in the state of Michigan and all its political subdivisions. Noninterest income mbwm_BusinessCombinationProFormaInformationProFormaNoninterestIncome Amount of pro forma noninterest income of combined entity as if acquisition date of business combination occurred as of beginning of period. Total capital minimum required for capital adequacy, amount Employee stock purchase plan Total capital, amount mbwm_BusinessCombinationRecognizedAssetAcquiredFinancingReceivableUnamortizedPurchasePremiumDiscount Business Combination, Recognized Asset Acquired, Financing Receivable, Unamortized Purchase Premium (Discount) Amount of unamortized purchase premium (discount) on financing receivable acquired in business combination and recognized at acquisition date, including PCD loans and Non-PCD loans. Other comprehensive income (loss): Eastern Michigan Bank Segment [Member] Represents Eastern Michigan Bank Segment. Collateralized Mortgage-Backed Securities [Member] Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table] us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan Dividend reinvestment plan us-gaap_DebtInstrumentFairValue Term note Mercantile Bank Segment [Member] Represents Mercantile Bank Segment. mbwm_BusinessCombinationRecognizedAssetAcquiredAssetIncludingGoodwill Business Combination, Recognized Asset Acquired, Asset Including Goodwill Amount of asset including goodwill acquired in business combination and recognized at acquisition date. us-gaap_NoninterestExpense Noninterest expense Total noninterest expense US Government Agency Debt Obligations and Mortgage Backed Securities [Member] This category includes information about debt securities issued by the United states and securities which are mortgage backed. us-gaap_DebtInstrumentFaceAmount Debt Instrument, Face Amount O 2026 Q1 Dividends [Member] Represents O 2026 Q1 Dividends. Modified in period Noninterest expense Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] us-gaap_RepurchaseAgreementCounterpartyWeightedAverageMaturityOfAgreements1 Repurchase Agreement Counterparty, Weighted Average Maturity of Agreements (Day) Financial Asset, Not Past Due [Member] mbwm_AccruedInterestPayableFairValueDisclosure Accrued interest payable Fair value portion of accrued interest payable. Total capital to be well capitalized, amount Employee stock purchase plan (in shares) Fair Value, Recurring and Nonrecurring [Table] Credit Loss, Financial Instrument [Policy Text Block] us-gaap_GoodwillPurchaseAccountingAdjustments Goodwill, Measurement Period Adjustment Dividend reinvestment plan (in shares) Debt Instrument, Name [Domain] Municipal General Obligation Bonds [Member] This category includes information about debt securities classified as municipal general obligation bonds. us-gaap_DebtInstrumentInterestRateStatedPercentage Debt Instrument, Interest Rate, Stated Percentage us-gaap_Depreciation Depreciation Average interest rate during the period Loans Categorized as 1-4 Family Mortgages [Member] Related to loans categorized as 1-4 family mortgages. Municipal Revenue Bonds [Member] This category includes information about debt securities classified as municipal revenue bonds. us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims Stock grants to directors for retainer fees Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member] Related to bonds issued or guaranteed by agencies of the U.S. federal government. us-gaap_DebtInstrumentPeriodicPaymentPrincipal Debt Instrument, Periodic Payment, Principal Bonds Issued by State-based Municipalities [Member] Related to bonds issued by state-based municipalities. Schedule of Long-Term Debt Instruments [Table] Debt Instrument [Axis] Common Stock Including Additional Paid in Capital [Member] Cash flows from operating activities us-gaap_UnrealizedGainLossOnDerivatives Net loss (gain) on instruments designated at fair value and related derivatives Cash flows from investing activities us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash from (for) operating activities Cash flows from financing activities us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash for investing activities Financing Receivable, Year One, Originated, Current Fiscal Year us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash from (for) financing activities us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt Purchases of securities available for sale us-gaap_LiabilitiesFairValueDisclosure Total liabilities Financing Receivable, Revolving us-gaap_AssetsFairValueDisclosure Total assets Financing Receivable, Held-for-Investment [Policy Text Block] Loans, Notes, Trade and Other Receivables Disclosure [Text Block] us-gaap_IncreaseDecreaseInDeposits Increase (Decrease) in Deposits Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member] Operating Segments [Member] Interest Rate Swap Fees [Member] Relating to interest rate swap fees. Accounting Policies [Abstract] Financing Receivable, Held-for-Sale [Policy Text Block] Segments [Domain] Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Product and Service, Revenue [Table] us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent Share-Based Compensation Arrangement by Share-Based Payment Award, Purchase Price of Common Stock, Percent US Treasury Securities [Member] Segments [Axis] us-gaap_StockRepurchasedDuringPeriodShares Stock Repurchased During Period, Shares (in shares) us-gaap_PaymentsForProceedsFromLoansAndLeases Loan originations and payments, net Income Statement [Abstract] Net increase (decrease) in all other deposits us-gaap_NumberOfOperatingSegments Number of Operating Segments us-gaap_NumberOfReportableSegments Number of Reportable Segments Net increase (decrease) in securities sold under agreements to repurchase Net increase (decrease) in time deposits Net income Net income Net income us-gaap_DividendsPayableDateOfRecordDayMonthAndYear Dividends Payable, Date of Record Financial Asset, Past Due [Member] us-gaap_GainLossOnSaleOfMortgageLoans Net gain from sales of mortgage loans held for sale Core deposit intangible amortization us-gaap_InterestIncomeExpenseNet Net interest income Unused lines of Credit [Member] Restricted Stock [Member] us-gaap_ProceedsFromStockPlans Employee stock purchase plan Noninterest-bearing us-gaap_FinancingReceivableNonaccrualInterestIncome Financing Receivable, Nonaccrual, Interest Income Accounting Standards Update and Change in Accounting Principle [Table] With no related allowance recorded, principal balance Occupancy Other expense Other Noninterest Expense Earnings on bank owned life insurance Earnings on bank owned life insurance us-gaap_NoninterestIncome Noninterest income Total noninterest income Noninterest income: us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss Debt Securities, Available-for-Sale, Allowance for Credit Loss Measurement Basis [Axis] Other income Fair Value Hierarchy and NAV [Domain] us-gaap_NoninterestIncomeOther Noninterest Income, Other us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate Share-Based Compensation Arrangement by Share-Based Payment Award, Discount from Market Price, Offering Date Measurement Frequency [Domain] us-gaap_ValuationAllowancesAndReservesBalance SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount, Ending Balance Statement of Financial Position [Abstract] us-gaap_DividendPayableDateToBePaidDayMonthAndYear Dividends Payable, Date to be Paid Deposit Liability [Table] Federal income taxes Other assets Repurchase Agreement, Counterparty [Table] Fair Value, Nonrecurring [Member] Fair Value, Recurring [Member] Common equity tier 1, amount Common equity tier 1 minimum required for capital adequacy, amount Document Type Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year Document Information [Line Items] Document Quarterly Report us-gaap_LesseeOperatingLeaseRenewalTerm Lessee, Operating Lease, Renewal Term (Year) us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1 Operating Lease, Weighted Average Remaining Lease Term (Year) Document Information [Table] Common equity tier 1 capital to be well capitalized, amount Entity Interactive Data Current Business Combination, Consideration Transferred, Equity Interest, Share Issued (in shares) Bank owned life insurance Financing Receivable, Originated, More than Five Years before Current Fiscal Year Document Transition Report us-gaap_IncreaseDecreaseInFinanceReceivables Increase (Decrease) in Finance Receivables Average diluted shares outstanding (in shares) Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year mbwm_InterestIncomeOnCommercialAndMortgageLoansDiscontinuedPeriod Interest Income on Commercial and Mortgage Loans Discontinued Period (Day) Number of days past due when interest income on commercial and mortgage loans is discontinued unless the loans are well-secured and in process of collection. mbwm_MaximumDelinquencyPeriodForConsumerAndCreditCardLoansToBeChargedOff Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged Off (Day) Maximum number of days delinquent for consumer and credit card loans to be charged off. Earnings per share (in dollars per share) us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic Net income us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss Average basic shares outstanding (in shares) Derivative Instrument [Axis] us-gaap_NotesReceivableNet Loans, net Basic earnings per share (in dollars per share) Consolidated Entities [Member] Title and Position [Domain] Debt Securities, Available-for-Sale [Table Text Block] us-gaap_Deposits Deposits Total deposits Earnings Per Share, Policy [Policy Text Block] Deposit Liabilities Disclosures [Text Block] us-gaap_GoodwillAcquiredDuringPeriod Goodwill, Acquired During Period Core deposit intangible Core deposit intangible, net Depreciation and amortization Document Fiscal Period Focus Document Fiscal Year Focus Amendment Flag Federal Home Loan Bank Branch [Domain] mbwm_BusinessCombinationBranchesAcquired Business Combination Branches Acquired The number of banking branches acquired in a business combination. Federal Home Loan Bank Branch [Axis] Financing Receivable, Past Due [Table] us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium Investment Income, Net, Amortization of Discount and Premium Goodwill Goodwill Document Period End Date Building [Member] Property, Plant, and Equipment [Text Block] Interest income Long-Lived Asset, Class [Domain] Legal Entity [Axis] us-gaap_InterestAndDividendIncomeOperating Interest income Total interest income Commercial Portfolio Segment [Member] Business Combination [Domain] us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment Financing Receivable, Individually Evaluated for Credit Loss Interest-bearing Entity File Number Entity Tax Identification Number Business Combination [Axis] Unallocated Financing Receivables [Member] Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss Entity [Domain] Entity Central Index Key us-gaap_FinancingReceivableAllowanceForCreditLosses Financing Receivable, Allowance for Credit Loss Allowance for credit losses Balance Balance Entity Registrant Name us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs Charge-offs Year-to-date gross write offs Performing Financial Instruments [Member] Entity Current Reporting Status Business Combination [Table] Money market Entity Incorporation, State or Country Code Business Combination, Pro Forma Information [Table Text Block] Land and Land Improvements [Member] Current Fiscal Year End Date Interest-bearing checking Entity Filer Category us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets Total identifiable assets acquired Time Deposits Entity Shell Company us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities Total identifiable liabilities acquired Entity Emerging Growth Company Nonperforming Financial Instruments [Member] Notional Amount Entity Small Business us-gaap_PaymentsForProceedsFromProductiveAssets Net purchases of premises and equipment and lease activity Savings us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet Net identifiable assets acquired Modified Derivative Assets Interest rate swaps Interest rate swaps us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment Premises and equipment us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles Core deposit intangible Interest expense Interest-earning deposits and Federal Funds sold Derivative Instruments and Hedging Activities Disclosure [Text Block] us-gaap_BusinessCombinationConsiderationTransferred1 Total consideration Deposits Entity Address, State or Province Entity Address, City or Town us-gaap_InterestExpenseOperating Interest expense Total interest expense Retained earnings Entity Address, Address Line One City Area Code Due in 2027 through 2031, amortized cost Due in 2032 through 2036, amortized cost Local Phone Number Due in 2026, amortized cost Entity Address, Postal Zip Code Derivative [Table] Accrued interest payable and other liabilities Preferred Stock [Member] No single maturity, fair value Title of 12(b) Security mbwm_FinancingReceivablesPrepaymentSpeedAssumed Financing Receivables, Prepayment Speed Assumed Percentage of prepayment speed assumed under financing receivables. Security Exchange Name mbwm_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment. Due in 2032 through 2036, fair value Trading Symbol Due in 2037 and beyond, fair value Derivatives, Policy [Policy Text Block] Due in 2026, fair value Due in 2027 through 2031, fair value Due in 2037 and beyond, amortized cost No single maturity, amortized cost Class of Stock [Axis] Consolidation, Eliminations [Member] Federal Home Loan Bank advances us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm Fair value Securities available for sale Debt Securities, Available-for-Sale Securities available for sale Recorded Balance 89 Days and Accruing Class of Financing Receivable [Axis] Class of Financing Receivable [Domain] Variable Rate [Domain] Entity Common Stock, Shares Outstanding Preferred stock, par value (in dollars per share) Executive Officer [Member] Financing Receivable, Credit Quality Indicator [Table] us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax Tax effect of unrealized holding gains (losses) on securities available for sale Unrealized holding gains (losses) on securities available for sale Total principal balance Internal Credit Assessment [Axis] Change in net unrealized holding gain (loss) on securities available for sale, net of tax effect Cash collateral, derivative liability Short-term borrowings Contractual amounts of financial instruments with off-balance sheet risk us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss Net interest income after provision for credit losses Cash collateral, derivative assets Subordinated debt and other borrowings Corporate and Bank Board Directors [Member] Represents Corporate and Bank Board Directors. Investments Classified by Contractual Maturity Date [Table Text Block] us-gaap_InterestIncomeDepositsWithFinancialInstitutions Other interest-earning assets Property, Plant, and Equipment [Table] Internal Credit Assessment [Domain] Common stock (924,999 shares issued at $48.55 per share) Securities, taxable Offsetting Assets and Liabilities [Table Text Block] Tabular disclosure of derivative and other financial assets and liabilities that are subject to offsetting, including master netting arrangements. Basis of Accounting, Policy [Policy Text Block] Securities, tax-exempt Derivative Contract [Domain] Long-Lived Asset, Class [Axis] Regulatory Capital Requirements under Banking Regulations [Text Block] Cash and due from banks us-gaap_Assets Total assets Total assets us-gaap_CashCashEquivalentsAndFederalFundsSold Total cash and cash equivalents Financing Receivable, Nonaccrual [Table] Eastern Michigan Bank [Member] Relating to Eastern Michigan Bank. us-gaap_CommonStockCapitalSharesReservedForFutureIssuance Common Stock, Capital Shares Reserved for Future Issuance (in shares) Loans Financing Receivable, before Allowance for Credit Loss Diluted earnings per share (in dollars per share) Revenue from Contract with Customer [Policy Text Block] us-gaap_IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights (in shares) Cash Debt Securities, Trading, and Equity Securities, FV-NI [Table] Service Charges on Deposit and Sweep Accounts [Member] Represents service charges on deposit and sweep accounts. Financing Receivable, Modified, Past Due [Table] Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff Schedule of Derivative Instruments [Table Text Block] Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block] Accounts and Financing Receivables [Table] Net amount, derivative assets Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Net amount, derivative liability Financing Receivable, Revolving, Writeoff Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff mbwm_LoansAndLeasesReceivablePercentagePeriodIncreaseDecrease Loans and Leases Receivable, Percentage Period Increase (Decrease) The percentage of increase or (decrease) during the period in loans and leases receivable during the period. Interest Interest Rate Swap [Member] Securities sold under agreements to repurchase The 2025 Employee Stock Purchase Plan [Member] Represents The 2025 Employee Stock Purchase Plan. Business Combination [Text Block] mbwm_SharebasedCompensationArrangementBySharebasedPaymentAwardMaximumEmployeePayrollDeduction Share-Based Compensation Arrangement by Share-Based Payment Award, Maximum Employee Payroll Deduction Maximum employee payroll deduction Share-Based Compensation Arrangement by Share-Based Payment Award, Minimum Employee Payroll Deduction us-gaap_StockholdersEquity Total shareholders’ equity Balances Balances Forfeited, weighted average fair value (in dollars per share) us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss Financing Receivable, Accrued Interest, after Allowance for Credit Loss us-gaap_PaymentsOfDividendsCommonStock Payment of cash dividends to common shareholders Vacant Land and Land Development and Residential Construction Loan [Member] Segment of the company's total financing receivables related to vacant land and land development and residential construction receivables. Commercial and Industrial [Member] Financing arrangement that represents a contractual right to receive money either on demand or on fixed or determinable dates related to commercial and industrial receivables. Real Estate Owner Occupied Loan [Member] Segment of the company's total financing receivables related to real estate owner occupied receivables. us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale Origination of mortgage loans held for sale Disclosure of Share-Based Compensation Arrangements by Share-Based Payment Award [Table Text Block] Real Estate Multi Family and Residential Rental Loan [Member] Segment of the company's total financing receivables related to real estate multi-family and residential rental loan receivables. us-gaap_OperatingLeaseRightOfUseAsset Operating Lease, Right-of-Use Asset Real Estate Non Owner Occupied Loan [Member] Segment of the company's total financing receivables related to real estate non owner occupied receivables. us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings Payoffs and paydowns of Federal Home Loan Bank advances Credit and Debit Card [Member] Retail Portfolio Segment [Member] Portfolio segment of the company's total financing receivables related to retail receivables. Schedule of Repurchase Agreements [Table Text Block] us-gaap_FinancingReceivableRevolvingConvertedToTermLoanDuringPeriod Financing Receivable, Revolving, Converted to Term Loan During Period ecd_Rule10b51ArrTrmntdFlag Rule 10b5-1 Arrangement Terminated [Flag] Property, Plant, and Equipment [Table Text Block] ecd_Rule10b51ArrAdoptedFlag Rule 10b5-1 Arrangement Adopted [Flag] Noninterest revenue Retail and Commercial Lines of Credit and Credit Card Receivables [Member] Related to retail and commercial lines of credit and credit card receivables. Commitments and contingent liabilities (Note 9) mbwm_CollateralDependentLoansFairValueDisclosure Collateral dependent loans The fair value disclosure of collateral dependent loans held by the company.