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Note 6 - Deposits (Details Textual) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Time Deposits, at or Above FDIC Insurance Limit | $ 570.0 | $ 477.0
Loans [Member] |  |
Deposit Overdrafts | $ 1.0 | $ 0.3

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- Definition Represents the proceeds from deposit overdrafts + References No definition available. + Details
Name: | mbwm_DepositOverdrafts
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount of time deposit liabilities, including certificates of deposit, in denominations that meet or exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 405 -Topic 942 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478353/942-405-50-1 + Details
Name: | us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_LoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |