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Note 1 - Summary of Significant Accounting Policies - Year-end Mortgage Loans Held for Sale (Details) - Mortgage Loans [Member] - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Mortgage loans held for sale	$ 15,824	$ 18,607
Less: Allowance to adjust to lower of cost or market	0	0
Mortgage loans held for sale, net	$ 15,824	$ 18,607

X

- Definition

Amount of allowance to adjust mortgage loans receivable held for sale to lower of cost or market price.

+ References

No definition available.

+ Details

Name:	mbwm_AllowanceToAdjustToLowerOfCostOrMarket
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount, before allowance to adjust to lower of cost or market, of mortgage loan receivables held-for-sale that are not part of a disposal group.

+ References

No definition available.

+ Details

Name:	mbwm_LoansReceivableHeldForSaleAmountNotPartOfDisposalGroupMortgage
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 948
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477011/948-310-45-1

+ Details

Name:	us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mbwm_MortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: