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Note 7 - Deposits (Details Textual) - USD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Time Deposits, at or Above FDIC Insurance Limit | $ 187.0 | $ 207.0
Loans [Member] |  |
Deposit Overdrafts | $ 0.9 | $ 0.1

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 405 -Section 50 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818 + 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: |