Note 3 - Loans and Allowance for Loan Losses - Nonaccrual Loans (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021
With no related allowance recorded, principal balance	$ 1,313,000	$ 15,715,000
With related allowance recorded, principal balance	6,415,000	3,651,000
Related allowance	2,283,000	546,000
Total principal balance	7,728,000	19,366,000
Commercial Portfolio Segment [Member]
With no related allowance recorded, principal balance	249,000	12,583,000
With related allowance recorded, principal balance	6,023,000	3,099,000
Related allowance	2,083,000	354,000
Total principal balance	6,272,000	15,682,000
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member]
With no related allowance recorded, principal balance	249,000	2,818,000
With related allowance recorded, principal balance	5,775,000	2,192,000
Related allowance	2,051,000	266,000
Commercial Portfolio Segment [Member] \| Vacant Land and Land Development and Residential Construction Loan [Member]
With no related allowance recorded, principal balance	0	0
With related allowance recorded, principal balance	0	0
Related allowance	0	0
Commercial Portfolio Segment [Member] \| Real Estate Owner Occupied Loan [Member]
With no related allowance recorded, principal balance	0	9,674,000
With related allowance recorded, principal balance	248,000	761,000
Related allowance	32,000	84,000
Commercial Portfolio Segment [Member] \| Real Estate Non Owner Occupied Loan [Member]
With no related allowance recorded, principal balance	0	0
With related allowance recorded, principal balance	0	146,000
Related allowance	0	4,000
Commercial Portfolio Segment [Member] \| Real Estate Multi Family and Residential Rental Loan [Member]
With no related allowance recorded, principal balance	0	91,000
With related allowance recorded, principal balance	0	0
Related allowance	0	0
Retail Portfolio Segment [Member]
With no related allowance recorded, principal balance	1,064,000	3,132,000
With related allowance recorded, principal balance	392,000	552,000
Related allowance	200,000	192,000
Total principal balance	1,456,000	3,684,000
Retail Portfolio Segment [Member] \| One to Four Family Mortgages [Member]
With no related allowance recorded, principal balance	1,064,000	2,025,000
With related allowance recorded, principal balance	392,000	412,000
Related allowance	200,000	$ 69,000
Retail Portfolio Segment [Member] \| Other Consumer Loans [Member]
With no related allowance recorded, principal balance	0
With related allowance recorded, principal balance	0
Related allowance	$ 0

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=mbwm_RetailPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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