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Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings (USD $) | Mar. 31, 2015 | Dec. 31, 2014
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Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | $ 5,384,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment | $ 5,793,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment
Commercial and Industrial [Member] | Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 13,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember | 16,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember
Vacant Land and Land Development and Residential Construction Loan [Member] | Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 232,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember | 151,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember
Real Estate Owner Occupied Loan [Member] | Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 168,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember | 182,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember
Real Estate Non Owner Occupied Loan [Member] | Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 4,394,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember | 4,778,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember
Real Estate Multi Family and Residential Rental Loan [Member] | Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 577,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember | 666,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember
Home Equity and Other [Member] | Retail Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 0 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember | 0 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember
1-4 Family Mortgages [Member] | Retail Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 0 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember | 0 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember
Commercial Portfolio Segment [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | 5,384,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember | 5,793,000 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember
Retail Loan [Member] |  |
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items] |  |
Allowance for losses, troubled debt restructurings | $ 0 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember | $ 0 us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember

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