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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
Note 4 - Loans and Allowance for Loan Losses (Details) - Allowance Related to Troubled Debt Restructurings [Line Items]
Allowance for losses, troubled debt restructurings	$ 5,384,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment	$ 5,793,000us-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	13,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialAndIndustrialMember	16,000us-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	232,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember	151,000us-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	168,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateOwnerOccupiedLoanMember	182,000us-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	4,394,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateNonOwnerOccupiedLoanMember	4,778,000us-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	577,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember	666,000us-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	0us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_HomeEquityAndOtherMember	0us-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	0us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_OneToFourFamilyMortgagesMember	0us-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	5,384,000us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = us-gaap_CommercialPortfolioSegmentMember	5,793,000us-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	$ 0us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember	$ 0us-gaap_AllowanceForCreditLossesChangeInMethodOfCalculatingImpairment / us-gaap_FinancingReceivablePortfolioSegmentAxis = mbwm_RetailLoanMember

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