Note 3 - Loans and Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2022
With no related allowance recorded, unpaid principal balance	$ 16,997,000
With no related allowance recorded, principal balance	15,715,000	$ 1,313,000
With no related allowance recorded, average recorded principal balance	19,857,000
With related allowance recorded, unpaid principal balance	3,671,000
With related allowance recorded, principal balance	3,651,000	6,415,000
Related allowance	546,000	2,283,000
With related allowance recorded, average recorded principal balance	3,440,000
Total unpaid principal balance	20,668,000
Total principal balance	19,366,000	7,728,000
Total average recorded principal balance	23,297,000
Commercial Portfolio Segment [Member]
With no related allowance recorded, unpaid principal balance	12,658,000
With no related allowance recorded, principal balance	12,583,000	249,000
With no related allowance recorded, average recorded principal balance	16,434,000
With related allowance recorded, unpaid principal balance	3,099,000
With related allowance recorded, principal balance	3,099,000	6,023,000
Related allowance	354,000	2,083,000
With related allowance recorded, average recorded principal balance	2,689,000
Total unpaid principal balance	15,757,000
Total principal balance	15,682,000	6,272,000
Total average recorded principal balance	19,123,000
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member]
With no related allowance recorded, unpaid principal balance	2,893,000
With no related allowance recorded, principal balance	2,818,000	249,000
With no related allowance recorded, average recorded principal balance	3,632,000
With related allowance recorded, unpaid principal balance	2,192,000
With related allowance recorded, principal balance	2,192,000	5,775,000
Related allowance	266,000	2,051,000
With related allowance recorded, average recorded principal balance	1,732,000
Commercial Portfolio Segment [Member] \| Vacant Land and Land Development and Residential Construction Loan [Member]
With no related allowance recorded, unpaid principal balance	0
With no related allowance recorded, principal balance	0	0
With no related allowance recorded, average recorded principal balance	0
With related allowance recorded, unpaid principal balance	0
With related allowance recorded, principal balance	0	0
Related allowance	0	0
With related allowance recorded, average recorded principal balance	0
Commercial Portfolio Segment [Member] \| Real Estate Owner Occupied Loan [Member]
With no related allowance recorded, unpaid principal balance	9,674,000
With no related allowance recorded, principal balance	9,674,000	0
With no related allowance recorded, average recorded principal balance	12,634,000
With related allowance recorded, unpaid principal balance	761,000
With related allowance recorded, principal balance	761,000	248,000
Related allowance	84,000	32,000
With related allowance recorded, average recorded principal balance	803,000
Commercial Portfolio Segment [Member] \| Real Estate Non Owner Occupied Loan [Member]
With no related allowance recorded, unpaid principal balance	0
With no related allowance recorded, principal balance	0	0
With no related allowance recorded, average recorded principal balance	131,000
With related allowance recorded, unpaid principal balance	146,000
With related allowance recorded, principal balance	146,000	0
Related allowance	4,000	0
With related allowance recorded, average recorded principal balance	154,000
Commercial Portfolio Segment [Member] \| Real Estate Multi Family and Residential Rental Loan [Member]
With no related allowance recorded, unpaid principal balance	91,000
With no related allowance recorded, principal balance	91,000	0
With no related allowance recorded, average recorded principal balance	37,000
With related allowance recorded, unpaid principal balance	0
With related allowance recorded, principal balance	0	0
Related allowance	0	0
With related allowance recorded, average recorded principal balance	0
Retail Portfolio Segment [Member]
With no related allowance recorded, unpaid principal balance	4,339,000
With no related allowance recorded, principal balance	3,132,000	1,064,000
With no related allowance recorded, average recorded principal balance	3,423,000
With related allowance recorded, unpaid principal balance	572,000
With related allowance recorded, principal balance	552,000	392,000
Related allowance	192,000	200,000
With related allowance recorded, average recorded principal balance	751,000
Total unpaid principal balance	4,911,000
Total principal balance	3,684,000	1,456,000
Total average recorded principal balance	4,174,000
Retail Portfolio Segment [Member] \| Home Equity and Other [Member]
With no related allowance recorded, unpaid principal balance	1,173,000
With no related allowance recorded, principal balance	1,107,000
With no related allowance recorded, average recorded principal balance	1,096,000
With related allowance recorded, unpaid principal balance	160,000
With related allowance recorded, principal balance	140,000
Related allowance	123,000
With related allowance recorded, average recorded principal balance	214,000
Retail Portfolio Segment [Member] \| One to Four Family Mortgages [Member]
With no related allowance recorded, unpaid principal balance	3,166,000
With no related allowance recorded, principal balance	2,025,000	1,064,000
With no related allowance recorded, average recorded principal balance	2,327,000
With related allowance recorded, unpaid principal balance	412,000
With related allowance recorded, principal balance	412,000	392,000
Related allowance	69,000	$ 200,000
With related allowance recorded, average recorded principal balance	$ 537,000

Average 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 15
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

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

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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 unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

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

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
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_HomeEquityAndOtherMember
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: