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Note 3 - Loans and Allowance for Loan Losses - Nonaccrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
With no related allowance recorded, principal balance	$ 1,346	$ 1,824
With related allowance recorded, principal balance	4,015	3,918
Related allowance	2,373	2,134
Total principal balance	5,361	5,742
Commercial Portfolio Segment [Member]
With no related allowance recorded, principal balance	66	657
With related allowance recorded, principal balance	2,232	2,110
Related allowance	1,850	1,732
Total principal balance	2,298	2,767
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
With no related allowance recorded, principal balance	25	615
With related allowance recorded, principal balance	2,232	2,110
Related allowance	1,850	1,732
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	41	42
With related allowance recorded, principal balance	0	0
Related allowance	0	0
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	0
Related allowance	0	0
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member]
With no related allowance recorded, principal balance	0	0
With related allowance recorded, principal balance	0	0
Related allowance	0	0
Retail Portfolio Segment [Member]
With no related allowance recorded, principal balance	1,280	1,167
With related allowance recorded, principal balance	1,783	1,808
Related allowance	523	402
Total principal balance	3,063	2,975
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
With no related allowance recorded, principal balance	1,280	1,167
With related allowance recorded, principal balance	1,783	1,808
Related allowance	523	402
Retail Portfolio Segment [Member] | Other Consumer Loans [Member]
With no related allowance recorded, principal balance	0	0
With related allowance recorded, principal balance	0	0
Related allowance	$ 0	$ 0

X

- Definition

Allowance of nonaccrual financing receivable.

+ References

No definition available.

+ Details

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

X

- Definition

Amortized cost of financing receivable on nonaccrual status with allowance for credit loss. Excludes net investment in lease.

+ References

No definition available.

+ Details

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

X

- Definition

Amortized cost of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

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Namespace Prefix:	us-gaap_
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X

- Definition

Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (2)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

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