XML 22 R50.htm IDEA: XBRL DOCUMENT v2.4.1.9
Note 4 - Loans and Allowance for Loan Losses (Details) - Loans Modified as Troubled Debt Restructurings (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Commercial:    
Loans modified, number of contracts   3us-gaap_FinancingReceivableModificationsNumberOfContracts2
Loans modified, pre-modification recorded principal balance   $ 368,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Loans modified, post-modification recorded principal balance   337,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Commercial and Industrial [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 6us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember		 1us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Loans modified, pre-modification recorded principal balance 568,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember		 14,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Loans modified, post-modification recorded principal balance 593,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember		 14,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Commercial and Industrial [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 1us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember		  
Loans modified, pre-modification recorded principal balance 79,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember		  
Loans modified, post-modification recorded principal balance 79,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember		  
Vacant Land and Land Development and Residential Construction Loan [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember		 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember		 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember		 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Vacant Land and Land Development and Residential Construction Loan [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember		  
Real Estate Owner Occupied Loan [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember		 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember		 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember		 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember
Real Estate Owner Occupied Loan [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 2us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember		  
Loans modified, pre-modification recorded principal balance 50,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember		  
Loans modified, post-modification recorded principal balance 50,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateOwnerOccupiedLoanMember		  
Real Estate Non Owner Occupied Loan [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember		 2us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember		 354,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember		 323,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember
Real Estate Non Owner Occupied Loan [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateNonOwnerOccupiedLoanMember		  
Real Estate Multi Family and Residential Rental Loan [Member] | Commercial Portfolio Segment [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 6us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Loans modified, pre-modification recorded principal balance 568,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Loans modified, post-modification recorded principal balance 593,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Real Estate Multi Family and Residential Rental Loan [Member] | Commercial Portfolio Segment [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 3us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Loans modified, pre-modification recorded principal balance 129,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Loans modified, post-modification recorded principal balance 129,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Real Estate Multi Family and Residential Rental Loan [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Real Estate Multi Family and Residential Rental Loan [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember		  
Home Equity and Other [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember		  
Home Equity and Other [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember		  
Home Equity and Other [Member]    
Commercial:    
Loans modified, number of contracts   0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember
Loans modified, pre-modification recorded principal balance   0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember
Loans modified, post-modification recorded principal balance   0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_HomeEquityAndOtherMember
1-4 Family Mortgages [Member] | Retail Loan [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
1-4 Family Mortgages [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
1-4 Family Mortgages [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember		  
1-4 Family Mortgages [Member]    
Commercial:    
Loans modified, number of contracts   0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember
Loans modified, pre-modification recorded principal balance   0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember
Loans modified, post-modification recorded principal balance   0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_OneToFourFamilyMortgagesMember
Commercial Portfolio Segment [Member] | Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts   3us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
Loans modified, pre-modification recorded principal balance   368,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
Loans modified, post-modification recorded principal balance   337,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
Retail Loan [Member] | Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember		  
Loans modified, pre-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember		  
Loans modified, post-modification recorded principal balance 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember		  
Retail Loan [Member]    
Commercial:    
Loans modified, number of contracts   0us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember
Loans modified, pre-modification recorded principal balance   0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember
Loans modified, post-modification recorded principal balance   0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivablePortfolioSegmentAxis
= mbwm_RetailLoanMember
Originated Loan [Member]    
Commercial:    
Loans modified, number of contracts 6us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember		  
Loans modified, pre-modification recorded principal balance 568,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember		  
Loans modified, post-modification recorded principal balance 593,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember		  
Acquired Loan [Member]    
Commercial:    
Loans modified, number of contracts 3us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember		  
Loans modified, pre-modification recorded principal balance 129,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember		  
Loans modified, post-modification recorded principal balance $ 129,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember