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Note 3 - Loans and Allowance for Loan Losses - Activity for Troubled Debt Restructurings (Details)	3 Months Ended
	Mar. 31, 2022 USD ($)
Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Beginning Balance	$ 4,973,000
Charge-Offs	0
Payments	(212,000)
Transfers to ORE	0
Net Additions/Deletions	(1,932,000)
Ending Balance	2,829,000
Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member]
Beginning Balance	0
Charge-Offs	0
Payments	0
Transfers to ORE	0
Net Additions/Deletions	0
Ending Balance	0
Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member]
Beginning Balance	10,435,000
Charge-Offs	0
Payments	(9,677,000)
Transfers to ORE	0
Net Additions/Deletions	(669,000)
Ending Balance	89,000
Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member]
Beginning Balance	146,000
Charge-Offs	0
Payments	(3,000)
Transfers to ORE	0
Net Additions/Deletions	0
Ending Balance	143,000
Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member]
Beginning Balance	91,000
Charge-Offs	0
Payments	(1,000)
Transfers to ORE	0
Net Additions/Deletions	0
Ending Balance	90,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Beginning Balance	627,000
Charge-Offs	0
Payments	(78,000)
Transfers to ORE	0
Net Additions/Deletions	1,797,000	[1]
Ending Balance	2,346,000
Retail Portfolio Segment [Member] | Other Consumer Loans [Member]
Beginning Balance	1,202,000
Charge-Offs	0
Payments	(2,000)
Transfers to ORE	0
Net Additions/Deletions	(1,187,000)	[1]
Ending Balance	$ 13,000
[1] Includes $1.2 million in the transfer of home equity lines of credit from other consumer loans to 1-4 family mortgages in association with the adoption of the CECL methodology effective January 1, 2022.

X

- Definition

A financing receivable which had its terms modified during the period and is now considered a troubled restructuring.

+ References

No definition available.

+ Details

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

X

- Definition

Reflects the amount of the charge-off related to a troubled debt restructuring.

+ References

No definition available.

+ Details

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

X

- Definition

The cash inflow associated with a financing receivable classified as a troubled debt restructuring.

+ References

No definition available.

+ Details

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

X

- Definition

The transfer of a financing receivable classified as a troubled debt restructuring to other real estate.

+ References

No definition available.

+ Details

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

X

- Definition

Accumulated amortized cost of financing receivable modified for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-42

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-33

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 310
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481746/310-40-50-4

+ Details

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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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- Details

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Data Type:	na
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- Details

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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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- Details

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