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Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans (USD $)	Mar. 31, 2015	Dec. 31, 2014
Nonperforming Financial Instruments [Member] | Commercial and Industrial [Member]
Note 4 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans [Line Items]
Nonperforming loans	$ 5,636,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember	$ 6,478,000mbwm_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	197,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember	209,000mbwm_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	17,467,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember	18,062,000mbwm_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	360,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember	378,000mbwm_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	23,747,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember	25,233,000mbwm_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	87,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember	106,000mbwm_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	762,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember	800,000mbwm_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	1,758,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember	3,399,000mbwm_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	2,520,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember	4,199,000mbwm_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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonaccrual loans	23,077,000us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	26,048,000us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonperforming loans	23,077,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	26,048,000mbwm_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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	26,000us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonaccrual loans	3,190,000us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	3,358,000us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember
Nonperforming loans	3,190,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	3,384,000mbwm_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	26,267,000mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans / us-gaap_FinancialInstrumentPerformanceStatusAxis = us-gaap_NonperformingFinancingReceivableMember	29,432,000mbwm_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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember	26,000us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember	0us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RetailLoanMember	26,000us-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	0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_OriginatedLoanMember	0us-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	$ 0us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing / us-gaap_FinancialInstrumentAxis = mbwm_AcquiredLoanMember	$ 26,000us-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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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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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

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