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Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans (USD $) | Mar. 31, 2015 | Dec. 31, 2014
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Nonperforming Financial Instruments [Member] | Commercial and Industrial [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | $ 5,636,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember | $ 6,478,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember
Nonperforming Financial Instruments [Member] | Vacant Land and Land Development and Residential Construction Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 197,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember | 209,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Nonperforming Financial Instruments [Member] | Real Estate Owner Occupied Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 17,467,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember | 18,062,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember
Nonperforming Financial Instruments [Member] | Real Estate Non Owner Occupied Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 360,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember | 378,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember
Nonperforming Financial Instruments [Member] | Real Estate Multi Family and Residential Rental Loan [Member] | Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 23,747,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember | 25,233,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Nonperforming Financial Instruments [Member] | Real Estate Multi Family and Residential Rental Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 87,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember | 106,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Nonperforming Financial Instruments [Member] | Home Equity and Other [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 762,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember | 800,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember
Nonperforming Financial Instruments [Member] | 1-4 Family Mortgages [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 1,758,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember | 3,399,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember
Nonperforming Financial Instruments [Member] | Retail Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 2,520,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember | 4,199,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember
Nonperforming Financial Instruments [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonaccrual loans | 23,077,000 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 26,048,000 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonperforming loans | 23,077,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 26,048,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonperforming Financial Instruments [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 26,000 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonaccrual loans | 3,190,000 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 3,358,000 us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonperforming loans | 3,190,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 3,384,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonperforming Financial Instruments [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Nonperforming loans | 26,267,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember | 29,432,000 mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Commercial and Industrial [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember
Commercial and Industrial [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember
Vacant Land and Land Development and Residential Construction Loan [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Vacant Land and Land Development and Residential Construction Loan [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Real Estate Owner Occupied Loan [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember
Real Estate Owner Occupied Loan [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember
Real Estate Non Owner Occupied Loan [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember
Real Estate Non Owner Occupied Loan [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember
Real Estate Multi Family and Residential Rental Loan [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Real Estate Multi Family and Residential Rental Loan [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Home Equity and Other [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember
Home Equity and Other [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember | 26,000 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember
1-4 Family Mortgages [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember
1-4 Family Mortgages [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember
Retail Loan [Member] | Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember
Retail Loan [Member] | Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember | 26,000 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember
Originated Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember | 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember
Acquired Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items] |  |
Loans past due 90 days or more still accruing interest | $ 0 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember | $ 26,000 us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember

X
- Definition Amount of financing receivables which are past due 90 days or more and still accruing interest and nonaccrual loans. + References No definition available. + Details
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Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: | mbwm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Recorded investment in financing receivables that are 90 days or more past due and still accruing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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