Document And Entity Information Note To Financial Statement Details Textual Significant Accounting Policies Note 1 - Summary of Significant Accounting Policies Note 3 - Securities Interest expense Note 4 - Loans and Allowance for Loan Losses Note 5 - Premises and Equipment, Net Note 6 - Mortgage Loan Servicing Note 7 - Core Deposit Intangible Assets, Net Note 8 - Deposits us-gaap_AvailableForSaleSecuritiesDebtSecurities Total available for sale securities Note 9 - Securities Sold Under Agreements to Repurchase Note 10 - Federal Home Loan Bank Advances Note 11 - Federal Income Taxes 2020 Note 12 - Stock-based Compensation 2019 Note 13 - Related Parties 2022 Total income Note 14 - Commitments and Off-balance-sheet Risk 2021 Interest and dividends from subsidiaries Total interest income Interest income Note 17 - Fair Values of Financial Instruments Note 18 - Fair Value Measurements Other interest-earning assets Note 19 - Earnings Per Share 2018 Fair Value Securities available for sale Available-for-sale Securities Note 20 - Subordinated Debentures Note 21 - Regulatory Matters Grades 5-7 [Member] A credit rating between 5 and 7. Note 23 - Quarterly Financial Data (Unaudited) Grades 1-4 [Member] A credit rating between 1 and 4. Note 24 - Mercantile Bank Corporation (Parent Company Only) Condensed Financial Statements Note 1 - Summary of Significant Accounting Policies - Year-end Mortgage Loans Held for Sale (Details) Grades 8-9 [Member] A credit rating between 8 and 9. Note 3 - Securities - Available-for-sale Securities (Details) Note 3 - Securities - Securities in a Continuous Loss Position (Details) Note 3 - Securities - Debt Securities by Maturity (Details) Note 4 - Loans and Allowance for Loan Losses - Components of Loan Portfolio (Details) Note 4 - Loans and Allowance for Loan Losses - Acquired Impaired Loans Accretable Yield (Details) mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits Total deposits The percentage of increase or (decrease) during the period in deposit liabilities. Note 4 - Loans and Allowance for Loan Losses - Concentrations Within the Loan Portfolio (Details) Note 4 - Loans and Allowance for Loan Losses - Nonperforming Loans (Details) Note 4 - Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans (Details) Note 4 - Loans and Allowance for Loan Losses - Impaired Loans (Details) us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End Note 4 - Loans and Allowance for Loan Losses - Loans by Credit Quality Indicators (Details) Note 4 - Loans and Allowance for Loan Losses - Retail Credit Exposure (Details) Note 4 - Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses and the Recorded Investments in Loans (Details) Note 4 - Loans and Allowance for Loan Losses - Loans Modified as Troubled Debt Restructurings (Details) Note 4 - Loans and Allowance for Loan Losses - Loans Modified As Troubled Debt Restructurings Within the Previous Twelve Months That Became Over 30 Days Past Due (Details) Note 4 - Loans and Allowance for Loan Losses - Activity for Troubled Debt Restructurings (Details) Note 4 - Loans and Allowance for Loan Losses - Allowance Related to Troubled Debt Restructurings (Details) Note 5 - Premises and Equipment, Net - Summary of Premises and Equipment (Details) Note 6 - Mortgage Loan Servicing - Mortgage Loans Serviced for Others (Details) Summary of Deposits and Percentage Change in Deposits [Table Text Block] Tabular disclosure of deposits and the percentage change in deposits. Note 6 - Mortgage Loan Servicing - Activity for Capitalized Mortgage Loan Servicing Rights (Details) Note 6 - Mortgage Loan Servicing - Estimated Amortization (Details) Note 7 - Core Deposit Intangible Assets, Net - Estimated Amortization Expense on Core Deposit Intangible Assets (Details) Securities, taxable mbwm_AggregateLocalDepositLiabilities Total local deposits Value of liabilities related to local deposits. Note 8 - Deposits - Summary of Deposits (Details) us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate Note 8 - Deposits - Maturity Distribution for Certificate of Deposits (Details) mbwm_OutOfAreaTimeDeposits100000AndOver 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. Securities, tax-exempt Note 8 - Deposits - Certificates of Deposit with Balances of $100,000 or More (Details) mbwm_OutOfAreaTimeDepositsUnder100000 Out-of-area time, under $100,000 The aggregate amount of out-of-area time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $100,000. Note 9 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) mbwm_PercentageOfNonInterestBearingDomesticDepositsToDepositsDemand Noninterest-bearing demand 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. Note 10 - Federal Home Loan Bank Advances - Maturities of Currently Outstanding FHLB Advances (Details) mbwm_AggregateOutOfAreaTimeDeposits Total out-of-area deposits Value of liabilities related to out-of-area time deposits. Note 11 - Federal Income Taxes - Consolidated Income Tax Expense (Details) mbwm_PercentageOfDomesticTimeDeposits100000AndOver Time, $100,000 and over The percentage of domestic time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more. Note 11 - Federal Income Taxes - Effective Income Tax Rate Reconciliation (Details) mbwm_PercentageOfDomesticTimeDepositsUnder100000 Time, under $100,000 The percentage of domestic time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $100,000. Note 11 - Federal Income Taxes - Effective Income Tax Rate Reconciliation (Details) (Parentheticals) Loans, including fees mbwm_PercentageOfOutOfAreaTimeDepositUnder100000 Out-of-area time, under $100,000 The percentage of out-of-area time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $100,000. Federal Home Loan Bank of Indianapolis [Member] Note 11 - Federal Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) Investment in bank subsidiary mbwm_AggregatePercentageOfLocalDeposits Total local deposits Represents a percentage of domestic deposit liabilities. mbwm_PercentageOfOutOfAreaTimeDeposits100000AndOver Out-of-area time, $100,000 and over 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. Note 12 - Stock-based Compensation - Summary of Restricted Stock Activity (Details) Note 12 - Stock-based Compensation - Summary of Stock Option Activity (Details) Note 12 - Stock-based Compensation - Stock Option Valuation Assumptions (Details) mbwm_AggregatePercentageOfDeposits Total deposits Represents a percentage of total deposits. mbwm_AggregatePercentageOfOutOfAreaDeposits Total out-of-area deposits Represents a percentage of out-of-area deposits Note 12 - Stock-based Compensation - Summary of Options Outstanding (Details) Note 12 - Stock-based Compensation - Summary of Information Related to Options Outstanding (Details) mbwm_PercentageOfIncreaseDecreaseInNonInterestBearingDemandDeposits Noninterest-bearing demand 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. Note 12 - Stock-based Compensation - Summary of Stock Option Grants and Exercises (Details) Federal Home Loan Bank Branch [Domain] Note 13 - Related Parties - Loans Outstanding to Directors and Executive Officers (Details) mbwm_PercentageOfIncreaseDecreaseInMoneyMarketDeposits Money market Percentage of increase or (decrease) in interest-bearing domestic money market demand account deposit liabilities. Federal Home Loan Bank Branch [Axis] Note 14 - Commitments and Off-balance-sheet Risk - Exposure to Credit Losses (Details) mbwm_PercentageOfIncreaseDecreaseOfInterestBearingCheckingDeposits Interest-bearing checking Percentage of increase or (decrease) in interest-bearing domestic checking deposit liabilities. mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDepositsUnder100000 Time, under $100,000 Percentage of increase or (decrease) in domestic time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $100,000. Note 14 - Commitments and Off-balance-sheet Risk - Instruments Carried at Fair Values (Details) mbwm_PercentageOfIncreaseOrDecreaseOfSavingsDeposits Savings Percentage of increase or (decrease) in interest-bearing domestic savings deposit liabilities. Saving deposits bear interest and have no stated maturity. Note 17 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) Federal Home Loan Bank Advances, Disclosure [Text Block] Note 18 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) mbwm_AggregatePercentageIncreaseDecreaseInLocalDeposits Total local deposits The percentage of increase or (decrease) during the period in domestic deposit liabilities. mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDeposits100000AndOver Time, $100,000 and over Percentage of increase or (decrease) in domestic time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more Note 18 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) Note 19 - Earnings Per Share - Computation of Earnings Per Share (Details) mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTime100000AndOver Out-of-area time, $100,000 and over 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. mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTimeUnder100000 Out-of-area time, under $100,000 Percentage of increase or (decrease) in out-of-area time deposits (including certificates of deposits, individual retirement accounts and open accounts) that total to less than $100,000. Note 20 - Subordinated Debentures - Business Trusts (Details) Note 21 - Regulatory Matters - Actual Capital Levels and Minimum Levels (Details) mbwm_AggregatePercentageIncreaseDecreaseInOutOfAreaDeposits Total out-of-area deposits The percentage of increase or (decrease) during the period in out-of-area deposit liabilities. Note 23 - Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Details) Note 24 - Mercantile Bank Corporation (Parent Company Only) Condensed Financial Statements - Condensed Balance Sheets (Details) Note 24 - Mercantile Bank Corporation (Parent Company Only) Condensed Financial Statements - Condensed Statements of Income (Details) Use of Estimates, Policy [Policy Text Block] Note 24 - Mercantile Bank Corporation (Parent Company Only) Condensed Financial Statements - Condensed Statement of Cash Flows (Details) Notes To Financial Statements Notes To Financial Statements [Abstract] New Accounting Pronouncements, Policy [Policy Text Block] Investments by Category [Axis] Reclassification, Policy [Policy Text Block] Marketable Securities and Investments Held at Cost [Domain] Interest income us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Consolidation, Policy [Policy Text Block] Director [Member] Subsequent Event [Member] us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsChecking Interest-bearing checking us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsSavings Savings us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsMoneyMarket Money market Related Party [Axis] Subsequent Event Type [Domain] Related Party [Domain] Subsequent Event Type [Axis] Cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash and due from banks Interest-earning deposits mbwm_ReserveOrLiabilityBalanceForFinancialInstrumentsWithOffBalanceSheetRisk Reserve or Liability Balance for Financial Instruments With Off Balance Sheet Risk The carrying amount for the reserve or liability for financial instruments with off-balance sheet risk. 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. mbwm_FeesAccretedIntoIncomeDuringInterestRateSwapAgreementsTerm Fees Accreted Into Income During Interest Rate Swap Agreements Term Period of time between issuance and maturity of interest rate swap agreements, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Pension and Other Postretirement Benefits Disclosure [Text Block] mbwm_FairValueOfInterestRateSwapAgreementLiability Fair Value of Interest Rate Swap Agreement Liability Fair value disclosure of the liability related to a derivative interest rate swap agreement. Consumer Other Financing Receivable 1 [Member] Class of financing receivables related to other consumer financing receivables. Over twelve months Six months to twelve months us-gaap_ConcentrationRiskPercentage1 Concentration Risk, Percentage us-gaap_TimeDeposits100000OrMore Total certificates of deposit Time, $100,000 and over mbwm_CashFairValueDisclosure Cash Fair value disclosure of cash held by the company. Three months to six months mbwm_AccruedInterestReceivableFairValueDisclosure Accrued interest receivable Fair value disclosure for interest which has been accrued but unpaid. Up to three months Efficiency program-related costs Amount of expenses recognized by efficiency program during the period. Concentration Risk Type [Domain] Payroll processing The income generate from providing payroll processing services to external customers. Letter of credit fees Amount of fees and commissions from letter of credit. Concentration Risk Type [Axis] Relationship to Entity [Domain] Title of Individual [Axis] In four to five years In one to two years In three to four years In two to three years Impaired loans The fair value disclosure of impaired loans held by the company. In one year or less Foreclosed assets The fair value disclosure of foreclosed assets held by the company. Stockholders' Equity, Total [Member] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Axis] Noninterest-bearing Noninterest-bearing demand Bank owned life insurance us-gaap_ServicingAssetAtAmortizedValue Balance at beginning of year Balance at end of year us-gaap_ServicingAssetAtFairValueAmount Servicing Asset at Fair Value, Amount us-gaap_InterestBearingDomesticDepositSavings Savings 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. us-gaap_InterestBearingDomesticDepositChecking Interest-bearing checking 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_InterestBearingDomesticDepositMoneyMarket Money market us-gaap_FinancingReceivableAllowanceForCreditLosses Beginning balance Ending balance 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. Preferred securities outstanding Preferred Securities of Subsidiary Trust Trust preferred securities possesses characteristics of both equity and debt issues and are generally issued by bank holding companies. us-gaap_ForeclosedAssets Foreclosed Assets us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit Time Deposits, at or Above FDIC Insurance Limit us-gaap_TimeDepositsLessThan100000 Time, under $100,000 Deposit Liabilities Disclosures [Text Block] us-gaap_DeferredTaxAssetsValuationAllowance Deferred Tax Assets, Valuation Allowance Valuation allowance us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount us-gaap_LoansAndLeasesReceivableAllowance Allowance for loan losses us-gaap_LoansAndLeasesReceivableNetReportedAmount Loans, net us-gaap_RepurchaseAgreementCounterpartyWeightedAverageMaturityOfAgreements1 Repurchase Agreement Counterparty, Weighted Average Maturity of Agreements us-gaap_DeferredTaxAssetsNet Deferred tax asset after valuation allowance Loans Ending balance us-gaap_LoansAndLeasesReceivableDeferredIncome Loans and Leases Receivable, Deferred Income mbwm_StockRepurchaseProgramAdditionalAuthorizedAmount Stock Repurchase Program Additional Authorized Amount Additional amount of stock repurchase plan authorized. Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Mercantile Bank Capital Trust I [Member] A business trust owned by the Company. Fund [Member] A pooled collateralized debt obligation. Other income us-gaap_DeferredIncomeTaxLiabilities Deferred tax liability us-gaap_DeferredTaxAssetsGross Deferred tax asset before valuation allowance Schedule of Repurchase Agreements [Table Text Block] us-gaap_NoninterestIncome Total noninterest income us-gaap_DeferredTaxAssetsLiabilitiesNet Total net deferred tax asset Bank [Member] This item represents the items associated with the Bank only. Other us-gaap_DeferredTaxAssetsOther Earnings on bank owned life insurance Earnings on bank owned life insurance 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. Noninterest income us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss Net interest income after provision for loan losses us-gaap_DeferredTaxAssetsDeferredIncome Deferred loan fees Provision for loan losses 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. us-gaap_NumberOfOperatingSegments Number of Operating Segments us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross Unrealized loss on securities Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block] us-gaap_DeferredTaxAssetsDerivativeInstruments Fair value of interest rate swap Net interest income Net interest income Mortgage Loan Derivatives, Policy [Policy Text Block] Disclosure of accounting policy for its mortgage loan derivative instruments. Mortgage Loans Held for Sale [Table Text Block] Tabular disclosure of year-end mortgage loans held for sale. Mortgage loans held for sale Amount, before allowance to adjust to lower of cost or market, of mortgage loan receivables held-for-sale that are not part of a disposal group. Bank Owned Life Insurance, Policy [Policy Text Block] Disclosure of accounting policy for bank owned life insurance. Credit and debit card fees Mortgage banking activities Federal Home Loan Bank stock mbwm_AllowanceToAdjustToLowerOfCostOrMarket Less: Allowance to adjust to lower of cost or market Amount of allowance to adjust mortgage loans receivable held for sale to lower of cost or market price. us-gaap_ValuationAllowancesAndReservesBalance Valuation Allowances and Reserves, Balance Fair Value of Financial Instruments, Policy [Policy Text Block] us-gaap_CashCashEquivalentsAndFederalFundsSold Total cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Service charges on deposit and sweep accounts Derivative Instruments and Hedging Activities Disclosure [Text Block] us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses Allowance for loan losses us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits Deferred compensation Mutual Funds [Member] This category includes information about securities classified as mutual fund. us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost Stock compensation Earnings Per Share, Policy [Policy Text Block] Comprehensive Income, Policy [Policy Text Block] us-gaap_DeferredTaxAssetsCapitalLossCarryforwards Deferred Tax Assets, Capital Loss Carryforwards Income Tax, Policy [Policy Text Block] Concentrations Within Loan Portfolio [Table Text Block] Tabular disclosure of concentrations within the loan portfolio. Commercial Real Estate Loans to Lessors of Non Residential Buildings [Member] Represents the company's commercial real estate loans to lessors of non-residential buildings. Deferred income tax assets mbwm_FinancingReceivableAllowanceForCreditLossesReversalOfRecovery Recoveries Amount of reversal of recovery of financing receivables doubtful of collection that were previously charged off. us-gaap_DeferredTaxLiabilitiesOther Other Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Amendment Flag us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets Core deposit intangible us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive Thereafter us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree 2020 Advertising Cost, Policy, Expensed Advertising Cost [Policy Text Block] us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo 2019 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive 2022 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour 2021 Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths 2018 Current Fiscal Year End Date us-gaap_DeferredTaxLiabilitiesMortgageServicingRights Mortgage loan servicing rights Document Fiscal Period Focus Document Fiscal Year Focus Reclassification of stranded tax effect related to available for sale securities resulting from Tax Cuts and Jobs Act Reclassification from AOCI to Retained Earnings, Current Period Amount of reclassification from AOCI to retained earnings during the current period. Deferred income tax liabilities Document Period End Date us-gaap_DeferredTaxLiabilitiesPrepaidExpenses Prepaid expenses us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment Depreciation Document Type Nature of Operation [Policy Text Block] Disclosure of accounting policy on nature of operations. mbwm_FairValueInputsDiscountFactor Fair Value Inputs, Discount Factor Discount factor used to further reduce the balance sheet carrying amount of property or other assets. Document Information [Line Items] Document Information [Table] Entity Public Float Mortgage Loans Serviced for Others [Table Text Block] Tabular disclosure on mortgage loan portfolios serviced for others. Entity Filer Category Federa lHome Loan Bank [Member] Represent Federal Home Loans Bank. Entity Current Reporting Status Mortgage Loan Servicing [Text Block] The entire disclosure for mortgage loans serviced for others. Entity Voluntary Filers mbwm_ContinuingInvolvementWithTransferredFinancialAssetsCustodialEscrowBalance Continuing Involvement with Transferred Financial Assets Custodial Escrow Balance Custodial escrow balances maintained in connection with serviced loans. Entity Well-known Seasoned Issuer 2018 mbwm_MortgageServicingRightsAmortizationExpenseNextTwelveMonths Amount of amortization expense for mortgage servicing rights expected to be recognized during the next fiscal year following the latest fiscal year. 2019 mbwm_MortgageServicingRightsAmortizationExpenseYearTwo Amount of amortization expense for mortgage servicing rights to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Federal Home Loan Mortgage Corporation [Member] Represent Federal Home Loan Mortgage Corporation. 2022 mbwm_MortgageServicingRightsAmortizationExpenseYearFive Amount of amortization expense for mortgage servicing rights expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Thereafter mbwm_MortgageServicingRightsAmortizationExpenseAfterYearFive Amount of amortization expense for mortgage servicing rights expected to be recognized after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Effect of federal tax law change Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability 2020 mbwm_MortgageServicingRightsAmortizationExpenseYearThree Amount of amortization expense for mortgage servicing rights expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. 2021 mbwm_MortgageServicingRightsAmortizationExpenseYearFour Amount of amortization expense for mortgage servicing rights expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Intangible Assets Disclosure [Text Block] Contractual Maturities of Certificates of Deposits of More than Specified Amount [Table Text Block] Tabular disclosure of the contractual maturities of certificates of deposits of more than specified amount. Contractual Maturities of Certificates of Deposits [Table Text Block] Tabular disclosure of the maturity distribution for certificates of deposit at year-end. Entity Central Index Key Entity Registrant Name Deferred income tax expense (benefit) Entity [Domain] Legal Entity [Axis] Current expense mbwm_EffectiveIncomeTaxReconciliationBankOwnedLifeInsurance Bank owned life insurance Amount of the difference between reported income tax expense (benefit) and expected tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from bank owned life insurance that is exempt from income taxes. mbwm_DeferredTaxAssetsFairValueWriteDownsOnForeclosedProperties Fair value write-downs on foreclosed properties Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from write-downs on foreclosed properties. mbwm_DeferredTaxLiabilitiesBusinessCombinationAdjustments Business combination adjustments Amount of deferred tax liability attributable to taxable temporary differences from business combination. mbwm_DeferredTaxAssetsNonAccrualLoanInterestIncome Nonaccrual loan interest income Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from nonaccrual loan interest income. Entity Common Stock, Shares Outstanding (in shares) Income Trading Symbol Comprehensive Income (Loss) Note [Text Block] Expenses Commitments and Contingencies, Policy [Policy Text Block] Total expenses The total amount of interest and other operating expenses for the period. mbwm_SharebasedCompensationArrangementBySharebasedPaymentAwardMinimumNumberOfSharesForMinimumVestingRights Share-based Compensation Arrangement by Share-based Payment Award, Minimum Number of Shares for Minimum Vesting Rights Represents the benchmark for the minimum number of shares awarded required for minimum vesting rights. mbwm_SharebasedCompensationArrangementBySharebasedPaymentAwardMaximumNumberOfSharesForMaximumVestingRights Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares for Maximum Vesting Rights Represents the benchmark for the maximum number of shares awarded required for maximum vesting rights. Schedule of Subordinated Borrowing [Table Text Block] Subordinated Borrowing, Name [Domain] Subordinated Borrowing [Axis] Goodwill and Intangible Assets, Policy [Policy Text Block] Directors and Executive Officers [Member] Represents the Directors and Executive officers of the company. mbwm_RelatedPartyDepositsAndRepurchaseAgreements Related Party Deposits and Repurchase Agreements Represents the balances of related party deposits and repurchase agreements. Subordinated Borrowings Disclosure [Text Block] mbwm_LoanCommitmentsToRelatedParties Loan Commitments to Related Parties Represents the amount of loan commitments to related parties of the Company. Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] First Bank Plans [Member] Compensation plans that originated with Firstbank. 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. FDIC insurance costs us-gaap_NoninterestExpense Total noninterest expenses Other expense mbwm_InterestExpenseDeferredCompensationPlan Interest Expense, Deferred Compensation Plan Represents the amount of interest expense incurred during the period related to deferred compensation plans. Stock Purchase Plan [Member] The Mercantile Bank Corporation Employee Stock Purchase Plan of 2014. 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. Furniture and equipment rent, depreciation and maintenance us-gaap_PropertyPlantAndEquipmentUsefulLife Property, Plant and Equipment, Useful Life Condensed Financial Information of Parent Company Only Disclosure [Text Block] Schedule of Share Based Compensation Arrangement by Share Based Payment Award Options Information Related to Stock Option Grants and Exercised [Table Text Block] Schedule of share based compensation arrangement by share based payment award options information related to stock option grants and exercised. mbwm_FairValueDiscountOfSubordinatedDebenturesRelatedToAssumedBusinessTrustsAtTimeAfMerger Fair Value Discount of Subordinated Debentures Related to Assumed Business Trusts at Time af Merger Represents the fair value discount of subordinated debentures related to assumed business trusts at the time of the merger. mbwm_NumberOfBusinessTrusts Number of Business Trusts Represents the Company's business trusts. ASSETS Noninterest expense mbwm_TermDebtSecuredByRealEstateBalloonPaymentPeriod Term Debt, Secured by Real Estate Balloon Payment, Period The period in which term debt becomes secured by a balloon payment. Exercise Price Range 1 [Member] Range 1 in a range of of exercise prices. Furniture and Fixtures [Member] mbwm_AmortizationOfFairValueDiscountRelatedToSubordinatedDebenturesOfAssumedBusinessTrusts Amortization of Fair Value Discount Related to Subordinated Debentures of Assumed Business Trusts Represents the annual amortization of the fair value discount related to subordinated debentures of assumed business trusts over a period of time. mbwm_AmortizationPeriodOfFairValueDiscountRelatedToSubordinatedDebenturesOfAssumedBusinessTrusts Amortization Period of Fair Value Discount Related to Subordinated Debentures of Assumed Business Trusts Represents the amortization period of the fair value discount related to subordinated debentures of assumed business trusts. Mortgage loans serviced for others Exercise Price Range 3 [Member] Range 3 in a range of of exercise prices. Net cash for financing activities Net cash from (for) financing activities Other Debt and Equity Securities [Member] Investments in debt and equity securities classified as other. Exercise Price Range 2 [Member] Range 2 in a range of of exercise prices. Land and Land Improvements [Member] Firstbank Capital Trust I [Member] A business trust owned by the Company. mbwm_InterestRatesOnLoansSecuredByNonRealEstateCollateral Interest Rates on Loans, Secured by Non-real Estate Collateral Stated interest rates on loans that are secured by non-real estate collateral. Net cash for investing activities Net cash for investing activities mbwm_AmortizationPeriodForTermDebtSecuredByRealEstate Amortization Period for Term Debt, Secured by Real Estate Amortization period for the payments related to a credit facility, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash from operating activities Net change in cash and cash equivalents Net change in cash and cash equivalents Firstbank Capital Trust III [Member] A business trust owned by the Company. Firstbank Capital Trust IV [Member] A business trust owned by the Company. Building Improvements [Member] Schedule of Share-based Compensation Shares Authorized Under Stock Option Plans Information Related to Option Outstanding [Table Text Block] Schedule of share based compensation shares authorized under stock option plans information related to option outstanding. Building [Member] Firstbank Capital Trust II [Member] A business trust owned by the Company. Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Axis] mbwm_TermDebtSecuredByNonRealEstateCollateralMaturityPeriod Term Debt Secured, by Non-real Estate Collateral Maturity Period Period of time between issuance and maturity of term debt secured by non-real estate collateral, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Property, Plant and Equipment, Policy [Policy Text Block] mbwm_AmountOfFederalReserveRequired Amount of Federal Reserve Required Amount of federal reserve requirement at period end that can be met with vault cash or deposits at a Federal Reserve Bank. Business Acquisition, Acquiree [Domain] Net cash from operating activities Business Acquisition [Axis] Transfers and Servicing of Financial Assets, Policy [Policy Text Block] us-gaap_PaymentsOfDividendsCommonStock Payment of cash dividends to common shareholders us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Derivatives, Policy [Policy Text Block] us-gaap_PaymentsForRepurchaseOfCommonStock Repurchase of common stock Repurchase and Resale Agreements Policy [Policy Text Block] us-gaap_ProceedsFromStockPlans Employee stock purchase plan Cash dividends per common share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Proceeds from stock option exercises, net of cashless exercises us-gaap_CommonStockDividendsPerShareDeclared Common Stock, Dividends, Per Share, Declared Off-Balance-Sheet Credit Exposure, Policy [Policy Text Block] Marketable Securities, Policy [Policy Text Block] us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod Impaired Financing Receivable, Interest Income, Cash Basis Method Related allowance us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod Impaired Financing Receivable, Interest Income, Accrual Method Dividend reinvestment plan Dividend reinvestment plan Total principal balance With related allowance recorded, principal balance Total average recorded principal balance With related allowance recorded, average recorded principal balance With no related allowance recorded, principal balance us-gaap_PaymentsForRepurchaseOfTrustPreferredSecurities Payments for Repurchase of Trust Preferred Securities Repurchase of trust preferred securities Total unpaid principal balance With related allowance recorded, unpaid principal balance With no related allowance recorded, average recorded principal balance Problem asset costs The costs that are associated with problem assets. With no related allowance recorded, unpaid principal balance Geographic Distribution [Domain] Geographic Distribution [Axis] Geographic Distribution, Domestic [Member] Asset Class [Axis] Asset Class [Domain] Residential Real Estate [Member] us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Average shares and dilutive potential common shares (in shares) us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Collateral [Domain] Collateral [Axis] Class of Financing Receivable, Type [Domain] Diluted earnings per common share (in dollars per share) Diluted (in dollars per share) Earnings per share diluted (in dollars per share) mbwm_NetGainLossFromSaleAndValuationWriteDownOfForeclosedAssets Net gain from sales and valuation write-downs of foreclosed assets The net gain or loss resulting from the sale and valuation write-down of foreclosed assets. Class of Financing Receivable, Type [Axis] Consumer Portfolio Segment [Member] Unallocated Financing Receivables [Member] Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Axis] us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings Maturities of Federal Home Loan Bank advances Commercial Portfolio Segment [Member] Weighted average common shares outstanding (in shares) Weighted average common shares outstanding for basic earnings per common share (in shares) us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Basic earnings per common share (in dollars per share) Basic (in dollars per share) Earnings per share basic (in dollars per share) Loans and Leases Receivable, Mortgage Banking Activities, Policy [Policy Text Block] Schedule of Financing Receivables, Non Accrual Status [Table Text Block] Loans and Leases Receivable, Troubled Debt Restructuring Policy [Policy Text Block] Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block] Finance, Loan and Lease Receivables, Held for Investments, Foreclosed Assets Policy [Policy Text Block] Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block] Finance, Loan and Lease Receivables, Held-for-sale, Policy [Policy Text Block] Cash and Cash Equivalents, Policy [Policy Text Block] Significant Accounting Policies [Text Block] us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval us-gaap_UnrecognizedTaxBenefits Unrecognized Tax Benefits Accounting Policies [Abstract] Parent Company [Member] Statement of Financial Position [Abstract] Consolidated Entities [Domain] Consolidated Entities [Axis] Consolidated Entities [Member] Condensed Cash Flow Statement [Table Text Block] Proceeds from Federal Home Loan Bank advances Statement of Cash Flows [Abstract] First Bank Employees [Member] Represents First Bank employees. Real Estate Dependent Loans and Foreclosed Assets Estimated Selling Costs [Member] Represents real estate dependent loans and foreclosed assets, estimated selling costs. Condensed Income Statement [Table Text Block] Statement of Stockholders' Equity [Abstract] Condensed Balance Sheet [Table Text Block] Quarterly Financial Information [Table Text Block] us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount Business Acquisition, Goodwill, Expected Tax Deductible Amount Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] invest_DerivativeNotionalAmount Derivative, Notional Amount Net decrease in securities sold under agreements to repurchase Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] mbwm_InterestIncomeOnCommercialAndMortgageLoansDiscontinuedPeriod Interest Income on Commercial and Mortgage Loans Discontinued Period 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 Maximum number of days delinquent for consumer and credit card loans to be charged off. Credit Facility [Domain] Net increase in all other deposits Credit Facility [Axis] Net decrease in time deposits Cash flows from financing activities Class of Stock [Axis] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Core Deposits [Member] Proceeds from bank owned life insurance cash value release and death benefits us-gaap_PaymentsToAcquireLifeInsurancePolicies Purchases of bank owned life insurance Finite-Lived Intangible Assets, Major Class Name [Domain] mbwm_BusinessCombinationBranchesAcquired Business Combination Branches Acquired The number of banking branches acquired in a business combination. Firstbank Corporation [Member] The entity of Firstbank Corporation. Finite-Lived Intangible Assets by Major Class [Axis] mbwm_BusinessAcquisitionConversionOfStockPerShare Business Acquisition Conversion of Stock Per Share The number of shares that each share of the acquiree is converted into shares of the acquirer. Other Tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate Effect of federal tax law change Change in valuation allowance us-gaap_LoansAndLeasesReceivableRelatedParties Loans and Leases Receivable, Related Parties Beginning balance Ending balance Net capital investment into subsidiaries us-gaap_IncomeTaxReconciliationTaxExemptIncome Tax-exempt interest Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] Business Combination Disclosure [Text Block] Tax at statutory rate (35%) Income Tax Disclosure [Text Block] Proceeds from maturities, calls and repayments of securities available for sale Proceeds from sales of securities available for sale Proceeds from Sale of Available-for-sale Securities us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Internal Credit Assessment [Domain] Internal Credit Assessment [Axis] us-gaap_PaymentsToAcquireAvailableForSaleSecurities Purchases of securities available for sale Add: Dilutive effects of share-based awards (in shares) us-gaap_PaymentsForProceedsFromProductiveAssets Purchases of premises and equipment, net mbwm_BusinessCombinationDebtAssumedNumberOfTrusts Business Combination Debt Assumed Number of Trusts The number of trusts for which debt assumed in a business combination are payable to. Net income attributable to common shares Net income Net income Net income attributable to common shares mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromFiveToTenYears Due from five to ten years The weighted average yield of a securities portfolio with due dates before 5 years and before 10 years. mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromOneToFiveYears Due from one to five years The weighted average yield of a securities portfolio with due dates after 1 year and before 5 years. mbwm_WeightedAverageYieldOfSecuritiesPortfolioNoSingleMaturity No single maturity, weighted average yield The weighted average yield of a securities portfolio with no single maturity date defined. mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueAftertenYears Due after ten years The weighted average yield of a securities portfolio with due dates after 10 years. mbwm_WeightedAverageYieldOfSecuritiesPortfolio Total available for sale securities The aggregate weighted average yield of a securities portfolio. Restricted Stock [Member] us-gaap_FinancingReceivableModificationsRecordedInvestment Beginning Balance Ending Balance Employee Stock Option [Member] Transfers from loans to foreclosed assets Schedule of Related Party Transactions [Table Text Block] us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1 Recorded Principal Balance us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1 Number of Contracts us-gaap_FinancingReceivableModificationsNumberOfContracts2 Number of Contracts Related Party Transactions Disclosure [Text Block] us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 Post- Modification Recorded Principal Balance us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 Pre- Modification Recorded Principal Balance Noncash financing and investing activities: Supplemental disclosures of cash flows information Federal income taxes Impaired Financing Receivables [Table Text Block] Troubled Debt Restructurings on Financing Receivables [Table Text Block] mbwm_MinimumNumberOfDaysPastDueAtPeriodEndForLoansModifiedAsTroubledDebtRestructurings Minimum Number of Days Past Due at Period End For Loans Modified as Troubled Debt Restructurings Represents the minimum number of days past due at period end for loans modified as troubled debt restructurings. Weighted average interest rate during the year Interest rate margin Debt Instrument, Basis Spread on Variable Rate Originated Loan [Member] A loan that was originated by the entity. Acquired Loan [Member] A loan that was acquired by the entity. 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. us-gaap_DebtInstrumentRepurchasedFaceAmount Debt Instrument, Repurchased Face Amount Nonperforming Financial Instruments [Member] Real Estate Owner Occupied Loan [Member] Segment of the company's total financing receivables related to real estate owner occupied receivables. 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. Financing Receivable Credit Quality Indicators [Table Text Block] 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_DebtInstrumentRepurchaseAmount Debt Instrument, Repurchase Amount Financial Instrument Performance Status [Domain] Financial Instrument Performance Status [Axis] Current loans Retail Portfolio Segment [Member] Portfolio segment of the company's total financing receivables related to retail receivables. Loans past due 90 days or more still accruing interest Nonaccrual loans Past due loans Earnings Per Share [Text Block] Earnings per common share: us-gaap_PaymentsForProceedsFromLoansAndLeases Loan originations and payments, net Financing Receivables, Equal to Greater than 90 Days Past Due [Member] Financing Receivables, 60 to 89 Days Past Due [Member] Proceeds from sales of foreclosed assets London Interbank Offered Rate (LIBOR) [Member] Financing Receivables, Period Past Due [Domain] Financing Receivables, Period Past Due [Axis] Financing Receivables, 30 to 59 Days Past Due [Member] Variable Rate [Domain] Variable Rate [Axis] Past Due Financing Receivables [Table Text Block] us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax Tax effect of fair value of interest rate swap Home Equity and Other [Member] Segment of the company's total financing receivables related to home equity and other receivables. One to Four Family Mortgages [Member] Segment of the company's total financing receivables related to 1-4 family mortgages. Percent of portfolio Percent of portfolio Loan portfolio classes and segments expressed as a percentage of the companies aggregate loans. Period increase (decrease) The percentage of increase or (decrease) during the period in loans and leases receivable net of deferred income. us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax Tax effect of unrealized holding gains (losses) on securities available for sale Schedule of Mortgage Servicing Rights Future Amortization Expense [Table Text Block] Tabular disclosure of the amount of amortization expense expected to be recorded in succeeding fiscal years for mortgage servicing rights. us-gaap_PaymentsToAcquireFederalHomeLoanBankStock Purchases of Federal Home Loan Bank stock us-gaap_PaymentsForProceedsFromFederalHomeLoanBankStock Proceeds from Federal Home Loan Bank stock redemption Cash flows from investing activities Reported Value Measurement [Member] Comprehensive income Comprehensive income Quarterly Financial Information [Text Block] us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity Line of Credit Facility, Remaining Borrowing Capacity Preferred stock, shares outstanding (in shares) Common stock, shares outstanding (in shares) us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity Line of Credit Facility, Maximum Borrowing Capacity Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Accretable Yield Movement [Table Text Block] Roll forward of the accretable yield for certain loans acquired with deteriorated credit quality not accounted for as debt securities. Total nonperforming loans Amount of financing receivables which are past due 90 days or more and still accruing interest and nonaccrual loans. us-gaap_DividendsCommonStockCash Cash dividends Maximum daily balance during the year Average daily balance during the year Weighted average interest rate at year-end us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue Stock-based compensation expense Change in other liabilities Accrued interest and other liabilities Share repurchase program (in shares) us-gaap_StockRepurchasedAndRetiredDuringPeriodValue Share repurchase program us-gaap_StockRepurchasedDuringPeriodShares Stock Repurchased During Period, Shares us-gaap_StockRepurchasedDuringPeriodValue Stock Repurchased During Period, Value us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets Other assets us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan Dividend reinvestment plan Dividend reinvestment plan (in shares) Junior Subordinated Debt [Member] us-gaap_AllocatedShareBasedCompensationExpense Allocated Share-based Compensation Expense Employee stock purchase plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Employee stock purchase plan us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment Ending balance: individually evaluated for impairment Stock option exercises (in shares) Exercised (in shares) us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet Accrued interest receivable us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment Ending balance: collectively evaluated for impairment Stock option exercises Ending balance: collectively evaluated for impairment Ending balance: individually evaluated for impairment Recoveries us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs Charge-offs us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Allowance for Credit Losses on Financing Receivables [Table Text Block] Stock grants to directors (in shares) Stock Issued During Period, Shares, Issued for Services Stock grants to directors for retainer fees Total liabilities and shareholders’ equity Total liabilities and shareholders’ equity Retained earnings Accumulated other comprehensive loss us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale Origination of mortgage loans held for sale us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Proceeds from sales of mortgage loans held for sale us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Fair Value, Measurements, Nonrecurring [Member] Fair Value, Measurements, Recurring [Member] Gain on trust preferred securities repurchase Gain on trust preferred securities repurchase Amount of gain (loss), from the difference between the repurchase price of the trust preferred securities initially issued by the entity or its subsidiaries and the net carrying amount of the debt at the time of its repurchase. Fair Value, Measurement Frequency [Domain] Measurement Frequency [Axis] mbwm_DiscountAccretionOnAcquiredLoans Accretion of acquired loans Represents the accretion of acquired loans recorded as interest income during the period. Net change in: Property, Plant and Equipment [Table Text Block] Property, Plant and Equipment Disclosure [Text Block] Deferred expense us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure Federal Home Loan Bank advances Common stock, no par value; 40,000,000 shares authorized; 16,592,125 shares outstanding at December 31, 2017 and 16,416,695 shares outstanding at December 31, 2016 us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure Securities sold under agreements to repurchase Common stock, shares authorized (in shares) us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations Subordinated debentures Stock grants to directors for retainer fee Stock grants to directors for retainer fees Common stock, par value (in dollars per share) Stock-based compensation expense us-gaap_ShareBasedCompensation us-gaap_CommonStockCapitalSharesReservedForFutureIssuance Common Stock, Capital Shares Reserved for Future Issuance Fair Value, Measurement Inputs, Disclosure [Text Block] Depreciation and amortization Preferred stock, no par value; 1,000,000 shares authorized; 0 shares outstanding at December 31, 2017 and December 31, 2016 us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent Other comprehensive income (loss), net of tax effect Preferred stock, par value (in dollars per share) us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 Total tax effect of other comprehensive income (loss) Preferred stock, shares authorized (in shares) us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent Total other comprehensive income (loss) us-gaap_Depreciation Depreciation Estimate of Fair Value Measurement [Member] Measurement Basis [Axis] Portion at Fair Value Measurement [Member] us-gaap_TreasuryStockAcquiredAverageCostPerShare Treasury Stock Acquired, Average Cost Per Share Fair value of interest rate swap us-gaap_StockRepurchaseProgramAuthorizedAmount1 Stock Repurchase Program, Authorized Amount Adjustments to reconcile net income to net cash from operating activities: Total Unrealized holding gains (losses) on securities available for sale us-gaap_LoansHeldForSaleFairValueDisclosure Loans held for sale Interest us-gaap_CashAndCashEquivalentsFairValueDisclosure Cash equivalents Shareholders' equity 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. Other comprehensive income (loss): Shareholders’ equity Total shareholders’ equity Balances Balances mbwm_NetGainLossFromSaleAndValuationWriteDownOfFormerBankPremises Net loss from sales and valuation write-downs of former bank premises The net gain or loss resulting from the sale and valuation write-down of former bank premises. Proceeds from sales of former bank premises The cash inflow from sale of former bank premises. Liabilities Total liabilities US Government Agencies Debt Securities [Member] Change in fair value of interest rate swap, net of tax effect Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Transfers from bank premises to other real estate owned Value transferred from bank premises to real estate owned (REO) in noncash transactions. us-gaap_DepositsFairValueDisclosure Deposits Cash flows from operating activities Contractual amounts of financial instruments with off-balance sheet risk Standby letters of credit, carrying value us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent Deferred Compensation Liability, Current and Noncurrent Standby letters of credit, contract amount Statement [Line Items] Schedule of Fair Value, Off-balance Sheet Risks [Table Text Block] us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued us-gaap_LoansReceivableFairValueDisclosure Loans, net us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure Federal Home Loan Bank stock Unused lines of Credit [Member] AOCI Attributable to Parent [Member] Change in net unrealized gain/(loss) on securities available for sale, net of tax effect Fair Value, by Balance Sheet Grouping [Table Text Block] Accrued interest and other liabilities Fair Value Disclosures [Text Block] Loan Origination Commitments [Member] Allowance Related to Loans Categorized as Troubled Debt Restructurings [Table Text Block] Tabular disclosure of the allowance related to loans categorized as troubled debt restructurings by loan class. Adjustments for New Accounting Principle, Early Adoption [Member] Trouble Debt Restructuring Activity [Table Text Block] Tabular disclosure of activity for loans modified as troubled debt restructurings. Includes charge-offs, payments, transfers to Other Real Estate and net additions/deletions. All Other States and Their Political Subdivisions [Member] States and their political subdivisions other than the State of Michigan and its political subdivision. State of Michigan and All Its Political Subdivisions [Member] Securities in the state of Michigan and all its political subdivisions. Interest rate swap agreement Securities Other Than US Government Agencies and the State of Michigan and Political Subdivisions [Member] Securities issued by issuers other than the US government and its agencies and the State of Michigan and all its political subdivisions. Securities Issued Concentration Risk [Member] Reflects the percentage of securities issued by one ore more significant issuer. Interest Rate Swap [Member] 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. mbwm_AccruedInterestPayableFairValueDisclosure Accrued interest payable Fair value portion of accrued interest payable. us-gaap_OperatingLeasesFutureMinimumPaymentsDue Operating Leases, Future Minimum Payments Due us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter Operating Leases, Future Minimum Payments, Due Thereafter Municipal General Obligation Bonds [Member] This category includes information about debt securities classified as municipal general obligation bonds. us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourAndFiveYears Operating Leases, Future Minimum Payments, Due in Four and Five Years Type of Adoption [Domain] us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoAndThreeYears Operating Leases, Future Minimum Payments, Due in Two and Three Years Adjustments for New Accounting Pronouncements [Axis] Municipal Revenue Bonds [Member] This category includes information about debt securities classified as municipal revenue bonds. us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent Operating Leases, Future Minimum Payments Due, Next Twelve Months Financial Instruments [Domain] Federal Home Loan Bank advances Long-term Federal Home Loan Bank Advances Financial Instrument [Axis] mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueInOneYearOrLess Due in one year or less The weighted average yield of securities portfolio with due dates in less than 1 year. Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 1 [Member] Retained Earnings [Member] Fair Value, Inputs, Level 3 [Member] Fair Value Hierarchy [Domain] Fair Value, Hierarchy [Axis] Subordinated debentures Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust Equity Component [Domain] Preferred Stock [Member] Common Stock [Member] Equity Components [Axis] Other Liabilities [Member] mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsChargeOffs Charge-Offs Reflects the amount of the charge-off related to a troubled debt restructuring. mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsPayments Payments The cash inflow associated with a financing receivable classified as a troubled debt restructuring. Net Additions/Deletions A financing receivable which had its terms modified during the period and is now considered a troubled restructuring. mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsTransferToOtherRealEstate Transfers to ORE The transfer of a financing receivable classified as a troubled debt restructuring to other real estate. Troubled Debt Restructurings on Financing Receivables with in Previous Twelve Months that Became Over Thirty Days Past Due [Table Text Block] Tabular disclosure for troubled debt restructurings on financing receivables within the previous twelve months that became over thirty days past due. us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis Available-for-sale Debt Securities, Amortized Cost Basis Securities sold under agreements to repurchase Outstanding balance at year-end Commitments Contingencies and Guarantees [Text Block] us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax Gross Unrealized Losses us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax Gross Unrealized Gains us-gaap_AvailableForSaleSecuritiesAmortizedCost Amortized Cost Securities available for sale, continuous unrealized loss position, unrealized loss Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 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 Balance Sheet Location [Domain] Balance Sheet Location [Axis] Scenario, Unspecified [Domain] Scenario, Forecast [Member] Scenario [Axis] us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Securities available for sale, continuous unrealized loss position, 12 months or more Securities available for sale, continuous unrealized loss position, less than 12 months Securities available for sale, continuous unrealized loss position Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block] Maximum [Member] Range [Domain] Weighted Average [Member] Minimum [Member] us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue No single maturity, fair value Range [Axis] us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue Due after ten years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue Due in one year or less us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue Due from five to ten years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue Due from one to five years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost No single maturity, amortized cost us-gaap_Deposits Total deposits Total deposits us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost Due after ten years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost Due from five to ten years Interest-bearing us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost Due from one to five years us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost Due in one year or less us-gaap_MortgageLoansOnRealEstateInterestRate Mortgage Loans on Real Estate, Interest Rate us-gaap_TimeDeposits Total certificates of deposit us-gaap_AvailableForSaleSecuritiesRestricted Available-for-sale Securities, Restricted Income before federal income tax expense Equity in undistributed net income of subsidiary Equity in undistributed net income of subsidiary Federal income tax expense Tax expense us-gaap_PolicyTextBlockAbstract Accounting Policies Debt Securities [Member] Available-for-sale Securities [Table Text Block] Major Types of Debt and Equity Securities [Domain] Statement [Table] Major Types of Debt and Equity Securities [Axis] Available-for-sale Securities [Member] Income Statement [Abstract] Award Type [Axis] Equity Award [Domain] us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment Related allowance Qualitative and Quantitative Information, Transferor's Continuing Involvement in Transferred Financial Assets, Transfer or Transferee [Domain] Qualitative and Quantitative Information, Transferor's Continuing Involvement, Transferred Financial Assets, by Transfer or Transferee [Axis] us-gaap_GainLossOnSaleOfSecuritiesNet Net (gain) loss from sales of available for sale securities Exercisable Number (in shares) Average remaining option term (years) (Year) Exercisable Weighted Average Exercise Price (in dollars per share) Outstanding Weighted Average Exercise Price (in dollars per share) Outstanding Number (in shares) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Maximum exercise price (in dollars per share) Minimum exercise price (in dollars per share) Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Exercise Price Range [Axis] Dividend yield Salaries and benefits us-gaap_DerivativeFairValueOfDerivativeLiability Interest rate swap Risk-free interest rate Expected stock price volatility us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance Valuation Allowance for Impairment of Recognized Servicing Assets, Balance Loss Contingency, Nature [Domain] Collateralized Mortgage Backed Securities [Member] Loss Contingency Nature [Axis] Expected option life (years) (Year) Commercial Real Estate [Member] Derivative Contract [Domain] Derivative Instrument [Axis] Forfeited (in dollars per share) Vested (in dollars per share) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue Nonvested at beginning of year (in dollars per share) Nonvested at end of year (in dollars per share) Additions us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Nonvested at beginning of year (in shares) Nonvested at end of year (in shares) us-gaap_GainLossOnSaleOfPropertyPlantEquipment Net loss from sales and disposals of premises and equipment us-gaap_ServicingAssetAtAmortizedValueAmortization1 Amortized to expense Granted (in dollars per share) Granted (in shares) Servicing Asset at Amortized Cost [Table Text Block] us-gaap_GainLossOnSaleOfMortgageLoans Net gain on sales of mortgage loans held for sale us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Forfeited (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested (in shares) us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueExpectedCreditLosses Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1 Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Weighted Average Life us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Aggregate intrinsic value of stock options exercised us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice Options exercisable at year-end (in dollars per share) Options exercisable at year-end (in shares) Weighted average per share fair value of stock options granted (in dollars per share) Counterparty Name [Domain] Counterparty Name [Axis] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Outstanding at beginning of year (in dollars per share) Outstanding at end of year (in dollars per share) us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield Balance at beginning of period Balance at end of period us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsToNonaccretableDifference Removal due to pool excess recovery Net reclassification from nonaccretable to accretable us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldDisposalsOfLoans Reductions us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroupMortgage Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage Mortgage loans held for sale, net us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice Forfeited or expired (in dollars per share) Additions us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice Granted (in dollars per share) us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion Accretion income us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice Exercised (in dollars per share) us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Outstanding at beginning of year (in shares) Outstanding at end of year (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod Forfeited or expired (in shares) New loans Advertising us-gaap_DefinedContributionPlanCostRecognized Defined Contribution Plan, Cost us-gaap_LoansAndLeasesReceivableRelatedPartiesProceeds Repayments us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans LIABILITIES AND SHAREHOLDERS' EQUITY Total assets Total assets us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Data processing Occupancy us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Loans, Notes, Trade and Other Receivables Disclosure [Text Block] us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1 Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Tier 1 capital to average assets, ratio Tier 1 capital to average assets to be well capitalized, ratio Tier 1 capital to average assets minimum required for capital adequacy, ratio Plan Name [Axis] Total capital to be well capitalized, ratio Total capital minimum required for capital adequacy, ratio Capital Required for Capital Adequacy to Risk Weighted Assets Common equity tier 1, ratio Plan Name [Domain] Other assets us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options Tier 1 capital to be well capitalized, ratio Total capital, ratio us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Standby Letters of Credit [Member] Tax benefit realized from stock option exercises 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, ratio Total capital, amount Core deposit intangible Finite-Lived Intangible Assets, Net Total capital to be well capitalized, amount Total capital minimum required for capital adequacy, amount us-gaap_FiniteLivedCoreDepositsGross Finite-Lived Core Deposits, Gross Tier 1 capital to average assets to be well capitalized, amount us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization Finite-Lived Intangible Assets, Accumulated Amortization Other operating expenses Common equity tier 1 capital to be well capitalized, amount Tier 1 capital to average assets, minimum required for capital adequacy, amount Tier 1 capital to average assets, amount Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Common equity tier 1 minimum required for capital adequacy, amount Statement of Comprehensive Income [Abstract] Common equity tier 1, amount Tier 1 capital, amount Tier 1 capital to be well capitalized, amount Tier 1 capital minimum required for capital adequacy, amount us-gaap_InterestExpense Total interest expense Interest expense Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Goodwill Goodwill Regulatory Capital Requirements under Banking Regulations [Text Block] Premises and equipment, net Total premises and equipment us-gaap_InterestExpenseDebt Interest Expense, Debt Less: accumulated depreciation Property, plant and equipment, gross Federal Home Loan Bank advances us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm Subordinated debentures and other borrowings Short-term borrowings us-gaap_TableTextBlock Notes Tables Deposits Thereafter