XML 152 R74.htm IDEA: XBRL DOCUMENT v2.4.1.9
Note 4 - Loans and Allowance for Loan Losses (Details) - Impaired Loans (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   $ 12,386,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
Commercial:    
Impaired loans, related allowance   12,386,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
Total impaired loans:    
Impaired loans, unpaid contractual principal balance   41,056,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Impaired loans, recorded principal balance   36,868,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
Impaired loans, related allowance   12,386,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
Impaired loans, average recorded principal balance   49,961,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Originated Loan [Member] | With No Related Allowance [Member] | Commercial and Industrial [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 1,170,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
2,229,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Impaired loans with no related allowance recorded, recorded principal balance 1,164,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
511,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Impaired loans with no related allowance recorded, average recorded principal balance 652,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
1,205,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Originated Loan [Member] | With No Related Allowance [Member] | Commercial Vacant Land and Land Development and Residential Construction Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 540,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
475,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Impaired loans with no related allowance recorded, recorded principal balance 209,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
362,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Impaired loans with no related allowance recorded, average recorded principal balance 227,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
991,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Originated Loan [Member] | With No Related Allowance [Member] | Commercial Real Estate Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 3,609,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
1,270,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Impaired loans with no related allowance recorded, recorded principal balance 1,901,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
785,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Impaired loans with no related allowance recorded, average recorded principal balance 4,365,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
1,084,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Originated Loan [Member] | With No Related Allowance [Member] | Commercial Real Estate Non Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 1,210,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
895,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Impaired loans with no related allowance recorded, recorded principal balance 1,210,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
733,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Impaired loans with no related allowance recorded, average recorded principal balance 971,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
4,049,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Originated Loan [Member] | With No Related Allowance [Member] | Commercial Real Estate Multi Family and Residential Rental Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 375,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
41,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Impaired loans with no related allowance recorded, recorded principal balance 317,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
1,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Impaired loans with no related allowance recorded, average recorded principal balance 64,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
390,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Originated Loan [Member] | With No Related Allowance [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 6,904,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
4,910,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans with no related allowance recorded, recorded principal balance 4,801,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
2,392,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans with no related allowance recorded, average recorded principal balance 6,279,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
7,719,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Originated Loan [Member] | With No Related Allowance [Member] | Retail Home Equity and Other [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 207,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
507,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Impaired loans with no related allowance recorded, recorded principal balance 191,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
461,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Impaired loans with no related allowance recorded, average recorded principal balance 517,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
471,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Originated Loan [Member] | With No Related Allowance [Member] | Retail 1-4 Family Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 1,144,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
1,272,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Impaired loans with no related allowance recorded, recorded principal balance 560,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
647,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Impaired loans with no related allowance recorded, average recorded principal balance 585,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
727,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Originated Loan [Member] | With No Related Allowance [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 1,351,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
1,779,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans with no related allowance recorded, recorded principal balance 751,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
1,108,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans with no related allowance recorded, average recorded principal balance 1,102,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
1,198,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Originated Loan [Member] | With No Related Allowance [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 8,255,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
6,689,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
Impaired loans with no related allowance recorded, recorded principal balance 5,552,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
3,500,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
Impaired loans with no related allowance recorded, average recorded principal balance 7,381,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
8,917,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
Commercial:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
Originated Loan [Member] | With An Allowance Recorded [Member] | Commercial and Industrial [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 1,578,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 5,299,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans with an allowance recorded, recorded principal balance 5,226,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans, related allowance 1,578,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans with an allowance recorded, average recorded principal balance 2,759,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Total impaired loans:    
Impaired loans, related allowance 1,578,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Commercial Vacant Land and Land Development and Residential Construction Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 151,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 2,000,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 2,000,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans, related allowance 151,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 3,229,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 151,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Commercial Real Estate Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 2,200,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 15,745,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 15,674,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans, related allowance 2,200,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 4,630,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 2,200,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Commercial Real Estate Non Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 4,779,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 16,033,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 15,949,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans, related allowance 4,779,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 18,245,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 4,779,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Commercial Real Estate Multi Family and Residential Rental Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 666,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 1,371,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 1,371,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans, related allowance 666,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 1,700,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 666,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 9,374,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 40,448,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans with an allowance recorded, recorded principal balance 40,220,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, related allowance 9,374,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans with an allowance recorded, average recorded principal balance 30,563,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Total impaired loans:    
Impaired loans, related allowance 9,374,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Retail Home Equity and Other [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 84,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 115,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans with an allowance recorded, recorded principal balance 84,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans, related allowance 84,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans with an allowance recorded, average recorded principal balance 128,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Total impaired loans:    
Impaired loans, related allowance 84,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Retail 1-4 Family Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 694,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 2,194,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans with an allowance recorded, recorded principal balance 2,000,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans, related allowance 694,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans with an allowance recorded, average recorded principal balance 2,115,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Total impaired loans:    
Impaired loans, related allowance 694,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Originated Loan [Member] | With An Allowance Recorded [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 778,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 2,309,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 2,084,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, related allowance 778,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 2,243,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 778,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Originated Loan [Member] | With An Allowance Recorded [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 10,152,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 42,757,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 42,304,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Impaired loans, related allowance 10,152,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 32,806,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 10,152,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Originated Loan [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 9,374,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Commercial:    
Impaired loans, related allowance 9,374,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Total impaired loans:    
Impaired loans, unpaid contractual principal balance 47,352,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, recorded principal balance 45,021,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, related allowance 9,374,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, average recorded principal balance 36,842,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Originated Loan [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 778,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Commercial:    
Impaired loans, related allowance 778,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Total impaired loans:    
Impaired loans, unpaid contractual principal balance 3,660,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, recorded principal balance 2,835,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, related allowance 778,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, average recorded principal balance 3,345,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Originated Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 10,152,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Commercial:    
Impaired loans, related allowance 10,152,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Total impaired loans:    
Impaired loans, unpaid contractual principal balance 51,012,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Impaired loans, recorded principal balance 47,856,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Impaired loans, related allowance 10,152,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Impaired loans, average recorded principal balance 40,187,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_OriginatedLoanMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Commercial and Industrial [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 1,586,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans with no related allowance recorded, recorded principal balance 1,579,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 563,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Commercial Vacant Land and Land Development and Residential Construction Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans with no related allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Commercial Real Estate Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 113,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans with no related allowance recorded, recorded principal balance 113,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 52,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Commercial Real Estate Non Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 326,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans with no related allowance recorded, recorded principal balance 326,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 260,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Commercial Real Estate Multi Family and Residential Rental Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 487,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans with no related allowance recorded, recorded principal balance 487,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 166,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 2,512,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans with no related allowance recorded, recorded principal balance 2,505,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 1,041,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Retail Home Equity and Other [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 641,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans with no related allowance recorded, recorded principal balance 639,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 262,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Retail 1-4 Family Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 866,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans with no related allowance recorded, recorded principal balance 866,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 458,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Acquired Loan [Member] | With No Related Allowance [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 1,507,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans with no related allowance recorded, recorded principal balance 1,505,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 720,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Acquired Loan [Member] | With No Related Allowance [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, unpaid contractual principal balance 4,019,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans with no related allowance recorded, recorded principal balance 4,010,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans with no related allowance recorded, average recorded principal balance 1,761,000us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Commercial:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithNoRelatedAllowanceMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Commercial and Industrial [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Commercial Vacant Land and Land Development and Residential Construction Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Commercial Real Estate Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 1,516,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 1,502,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 501,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Commercial Real Estate Non Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Commercial Real Estate Multi Family and Residential Rental Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 1,516,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans with an allowance recorded, recorded principal balance 1,502,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans with an allowance recorded, average recorded principal balance 501,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Total impaired loans:    
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Retail Home Equity and Other [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Retail 1-4 Family Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Acquired Loan [Member] | With An Allowance Recorded [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance 1,516,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans with an allowance recorded, recorded principal balance 1,502,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans with an allowance recorded, average recorded principal balance 501,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Total impaired loans:    
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Acquired Loan [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Commercial:    
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Total impaired loans:    
Impaired loans, unpaid contractual principal balance 4,028,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, recorded principal balance 4,007,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Impaired loans, average recorded principal balance 1,542,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Acquired Loan [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Commercial:    
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Total impaired loans:    
Impaired loans, unpaid contractual principal balance 1,507,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, recorded principal balance 1,505,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, related allowance 0us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Impaired loans, average recorded principal balance 720,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
 
Acquired Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Commercial:    
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Total impaired loans:    
Impaired loans, unpaid contractual principal balance 5,535,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans, recorded principal balance 5,512,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans, related allowance 605,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
Impaired loans, average recorded principal balance 2,262,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancialInstrumentAxis
= mbwm_AcquiredLoanMember
 
With An Allowance Recorded [Member] | Commercial and Industrial [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   792,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   1,517,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Impaired loans with an allowance recorded, recorded principal balance   1,440,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Impaired loans, related allowance   792,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Impaired loans with an allowance recorded, average recorded principal balance   1,880,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
Total impaired loans:    
Impaired loans, related allowance   792,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialAndIndustrialMember
With An Allowance Recorded [Member] | Commercial Vacant Land and Land Development and Residential Construction Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   844,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   4,436,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Impaired loans with an allowance recorded, recorded principal balance   4,139,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Impaired loans, related allowance   844,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Impaired loans with an allowance recorded, average recorded principal balance   3,354,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Total impaired loans:    
Impaired loans, related allowance   844,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialVacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
With An Allowance Recorded [Member] | Commercial Real Estate Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   528,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   1,513,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Impaired loans with an allowance recorded, recorded principal balance   1,513,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Impaired loans, related allowance   528,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Impaired loans with an allowance recorded, average recorded principal balance   2,550,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
Total impaired loans:    
Impaired loans, related allowance   528,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateOwnerOccupiedLoanMember
With An Allowance Recorded [Member] | Commercial Real Estate Non Owner Occupied Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   7,969,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   21,088,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Impaired loans with an allowance recorded, recorded principal balance   21,072,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Impaired loans, related allowance   7,969,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Impaired loans with an allowance recorded, average recorded principal balance   28,388,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
Total impaired loans:    
Impaired loans, related allowance   7,969,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateNonOwnerOccupiedLoanMember
With An Allowance Recorded [Member] | Commercial Real Estate Multi Family and Residential Rental Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   1,127,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   3,219,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Impaired loans with an allowance recorded, recorded principal balance   2,684,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Impaired loans, related allowance   1,127,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Impaired loans with an allowance recorded, average recorded principal balance   2,915,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
Total impaired loans:    
Impaired loans, related allowance   1,127,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_CommercialRealEstateMultiFamilyAndResidentialRentalLoanMember
With An Allowance Recorded [Member] | Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   11,260,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   31,773,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans with an allowance recorded, recorded principal balance   30,848,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans, related allowance   11,260,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans with an allowance recorded, average recorded principal balance   39,087,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Total impaired loans:    
Impaired loans, related allowance   11,260,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
With An Allowance Recorded [Member] | Retail Home Equity and Other [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   96,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   320,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Impaired loans with an allowance recorded, recorded principal balance   289,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Impaired loans, related allowance   96,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Impaired loans with an allowance recorded, average recorded principal balance   329,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
Total impaired loans:    
Impaired loans, related allowance   96,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailHomeEquityAndOtherMember
With An Allowance Recorded [Member] | Retail 1-4 Family Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   1,030,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   2,274,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Impaired loans with an allowance recorded, recorded principal balance   2,231,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Impaired loans, related allowance   1,030,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Impaired loans with an allowance recorded, average recorded principal balance   1,628,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
Total impaired loans:    
Impaired loans, related allowance   1,030,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_Retail1To4FamilyMortgagesMember
With An Allowance Recorded [Member] | Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   1,126,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   2,594,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans with an allowance recorded, recorded principal balance   2,520,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans, related allowance   1,126,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans with an allowance recorded, average recorded principal balance   1,957,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Total impaired loans:    
Impaired loans, related allowance   1,126,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
With An Allowance Recorded [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   12,386,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
Commercial:    
Impaired loans with an allowance recorded, unpaid contractual principal balance   34,367,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
Impaired loans with an allowance recorded, recorded principal balance   33,368,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
Impaired loans, related allowance   12,386,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
Impaired loans with an allowance recorded, average recorded principal balance   41,044,000us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
Total impaired loans:    
Impaired loans, related allowance   12,386,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= mbwm_WithAnAllowanceRecordedMember
Commercial Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   11,260,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Commercial:    
Impaired loans, related allowance   11,260,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Total impaired loans:    
Impaired loans, unpaid contractual principal balance   36,683,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans, recorded principal balance   33,240,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans, related allowance   11,260,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans, average recorded principal balance   46,806,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Retail Loan [Member]    
Financing Receivable, Impaired [Line Items]    
Impaired loans with no related allowance recorded, related allowance   1,126,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Commercial:    
Impaired loans, related allowance   1,126,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Total impaired loans:    
Impaired loans, unpaid contractual principal balance   4,373,000us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans, recorded principal balance   3,628,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans, related allowance   1,126,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember
Impaired loans, average recorded principal balance   $ 3,155,000us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= mbwm_RetailLoanMember