Note 3 - Loans and Allowance for Loan Losses - Activity for Troubled Debt Restructurings (Details) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member]
Beginning Balance	$ 6,414,000	$ 8,587,000	$ 14,138,000
Charge-Offs	(17,000)	0	0
Payments	(4,278,000)	(11,260,000)	(20,364,000)
Transfers to ORE	0	0	0
Net Additions/Deletions	2,854,000	9,087,000	14,813,000
Ending Balance	4,973,000	6,414,000	8,587,000
Commercial Portfolio Segment [Member] \| Vacant Land and Land Development and Residential Construction Loan [Member]
Beginning Balance	0	85,000	0
Charge-Offs	0	0	0
Payments	0	(85,000)	(2,000)
Transfers to ORE	0	0	0
Net Additions/Deletions	0	0	87,000
Ending Balance	0	0	85,000
Commercial Portfolio Segment [Member] \| Real Estate Owner Occupied Loan [Member]
Beginning Balance	14,797,000	1,145,000	3,100,000
Charge-Offs	0	0	0
Payments	(5,048,000)	(3,765,000)	(3,820,000)
Transfers to ORE	0	0	(97,000)
Net Additions/Deletions	686,000	17,417,000	1,962,000
Ending Balance	10,435,000	14,797,000	1,145,000
Commercial Portfolio Segment [Member] \| Real Estate Non Owner Occupied Loan [Member]
Beginning Balance	480,000	178,000	210,000
Charge-Offs	0	0	0
Payments	(334,000)	(585,000)	(32,000)
Transfers to ORE	0	0	0
Net Additions/Deletions	0	887,000	0
Ending Balance	146,000	480,000	178,000
Commercial Portfolio Segment [Member] \| Real Estate Multi Family and Residential Rental Loan [Member]
Beginning Balance	0	7,000	24,000
Charge-Offs	0	0	0
Payments	(1,000)	(7,000)	(17,000)
Transfers to ORE	0	0	0
Net Additions/Deletions	92,000	0	0
Ending Balance	91,000	0	7,000
Retail Portfolio Segment [Member] \| Home Equity and Other [Member]
Beginning Balance	1,146,000	1,415,000	1,402,000
Charge-Offs	0	0	(18,000)
Payments	(426,000)	(881,000)	(272,000)
Transfers to ORE	0	0	0
Net Additions/Deletions	482,000	612,000	303,000
Ending Balance	1,202,000	1,146,000	1,415,000
Retail Portfolio Segment [Member] \| One to Four Family Mortgages [Member]
Beginning Balance	806,000	724,000	578,000
Charge-Offs	0	0	0
Payments	(224,000)	(68,000)	(162,000)
Transfers to ORE	0	0	0
Net Additions/Deletions	45,000	150,000	308,000
Ending Balance	$ 627,000	$ 806,000	$ 724,000

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

No definition available.

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

- 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

- 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

- 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

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

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