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Note 4 - Loans and Allowance for Loan Losses (Details) - Concentrations Within the Loan Portfolio (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Note 4 - Loans and Allowance for Loan Losses (Details) - Concentrations Within the Loan Portfolio [Line Items]
Commercial real estate loans to lessors of non-residential buildings	$ 2,089,277,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome	$ 1,053,243,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome	$ 1,041,189,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Commercial Real Estate Loans to Lessors of Non-Residential Buildings [Member]
Note 4 - Loans and Allowance for Loan Losses (Details) - Concentrations Within the Loan Portfolio [Line Items]
Commercial real estate loans to lessors of non-residential buildings	$ 480,170,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialRealEstateLoansToLessorsOfNonResidentialBuildingsMember	$ 299,446,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialRealEstateLoansToLessorsOfNonResidentialBuildingsMember
Commercial real estate loans to lessors of non-residential buildings	23.00%mbwm_LoanPortfolioClassesAndSegmentsAsPercentageOfAggregateLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialRealEstateLoansToLessorsOfNonResidentialBuildingsMember	28.40%mbwm_LoanPortfolioClassesAndSegmentsAsPercentageOfAggregateLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = mbwm_CommercialRealEstateLoansToLessorsOfNonResidentialBuildingsMember

X

- Definition

Loan portfolio classes and segments as a percentage of aggregate loans.

+ References

No definition available.

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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