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Note 20 - Subordinated Notes (Details Textual) - Subordinated Notes [Member] - USD ($) $ in Millions | Jan. 14, 2022 | Dec. 15, 2021
--- | --- | ---
Subordinated Debt, Principal Amount |  | $ 75
Subordinated Borrowing, Interest Rate |  | 3.25%
Subordinated Borrowing, Redemption Price, Percentage of Principal Amount |  | 100.00%
Increase to Equity Capital From Issuance of Subordinated Long-term Debt |  | $ 70
Subsequent Event [Member] |  |
Subordinated Debt, Principal Amount | $ 15 |
Increase to Equity Capital From Issuance of Subordinated Long-term Debt | $ 15 |
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument, Basis Spread on Variable Rate |  | 2.12%

X
- Definition The amount of increase to equity capital from the issuance of subordinated long-term debt. + References No definition available. + Details
Name: | mbwm_IncreaseToEquityCapitalFromIssuanceOfSubordinatedLongtermDebt
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Redemption price as a percentage of principal amount. + References No definition available. + Details
Name: | mbwm_SubordinatedBorrowingRedemptionPricePercentageOfPrincipalAmount
Namespace Prefix: | mbwm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Principal amount of subordinated debt. + References No definition available. + Details
Name: | mbwm_SubordinatedDebtPrincipalAmount
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Stated interest rate of the subordinated debt. + References No definition available. + Details
Name: | us-gaap_SubordinatedBorrowingInterestRate
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SubordinatedBorrowingAxis=mbwm_SubordinatedNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |