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Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis (USD $) | Dec. 31, 2014 | Dec. 31, 2013
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Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | $ 432,912,000 us-gaap_AvailableForSaleSecurities | [1] | $ 131,178,000 us-gaap_AvailableForSaleSecurities | [1]
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |  |
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 193,468,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |  |
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 98,477,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |  |
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 193,468,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  |  |
US Government Agencies Debt Securities [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 193,468,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |  | 98,477,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |  |  |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 93,561,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |  |  |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 13,558,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |  |  |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 93,561,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |  |  |
Collateralized Mortgage Backed Securities [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 93,561,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |  | 13,558,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember |
Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |  |  |
Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |
Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 122,801,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |  |  |
Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 16,872,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |
Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 10,281,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |  |  |
Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |
Municipal General Obligation Bonds [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 133,082,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |  |  |
Municipal General Obligation Bonds [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 133,082,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |  | 16,872,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalGeneralObligationBondsMember |
Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |  |  |
Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |
Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 10,873,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |  |  |
Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 916,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |
Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |  |  |
Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |
Municipal Revenue Bonds [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 10,873,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |  |  |
Municipal Revenue Bonds [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 10,873,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |  | 916,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MunicipalRevenueBondsMember |
Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |  |  |
Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 1,928,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |  |  |
Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |  |  |
Other Debt Obligations [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 1,928,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |  |  |
Other Debt Obligations [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities | 1,928,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |  |  |
Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MutualFundsMember |
Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 1,355,000 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MutualFundsMember |
Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 0 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MutualFundsMember |
Mutual Funds [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Available for sale securities |  |  | 1,355,000 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_MutualFundsMember |
Fair Value, Inputs, Level 1 [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Derivative | 0 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Assets and Liabilities measured at fair value on recurring basis | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Derivative | (253,000)us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (264,000)us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Assets and Liabilities measured at fair value on recurring basis | 422,378,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 130,914,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Derivative | 0 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Assets and Liabilities measured at fair value on recurring basis | 10,281,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Derivative | (253,000)us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (264,000)us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring [Member] |  |  |  |
Note 18 - Fair Values Measurements (Details) - Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items] |  |  |  |
Assets and Liabilities measured at fair value on recurring basis | $ 432,659,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | $ 130,914,000 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
[1] | See Note 18 for a description of the fair value hierarchy as well as a disclosure of levels for classes of financial assets and liabilities.

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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