Conversion ratio of acuiree's common stock converted into acquire's common stock in business combination.

No definition available.

Name:	mbwm_BusinessCombinationAcquireesCommonStockConversionToAcquiresCommonStockRatio
Namespace Prefix:	mbwm_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Per share price of acquiree's common stock will be converted in business combination.

+ References

No definition available.

+ Details

Name:	mbwm_BusinessCombinationAcquireesCommonStockConversionToCashRatio
Namespace Prefix:	mbwm_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 805
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479328/805-10-50-8

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 805
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 41
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479303/805-10-55-41

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479581/805-30-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479581/805-30-50-1

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

+ Details

Name:	us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the declared dividend will be paid, in YYYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-3

+ Details

Name:	us-gaap_DividendPayableDateToBePaidDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the dividend to be paid was declared, in YYYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DividendsPayableDateDeclaredDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the holder must own the stock to be entitled to the dividend, in YYYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_DividendsPayableDateOfRecordDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=mbwm_EasternMichiganFinancialCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DividendsAxis=mbwm_O2025Q3DividendsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 14 - Subsequent Events (Details Textual) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	Jul. 22, 2025 USD ($) $ / shares	Jul. 17, 2025 $ / shares	Jun. 30, 2025 $ / shares	Jun. 30, 2024 $ / shares	Jun. 30, 2025 $ / shares	Jun. 30, 2024 $ / shares	Jul. 21, 2025 $ / shares
Common Stock, Dividends, Per Share, Cash Paid (in dollars per share)			$ 0.37	$ 0.35	$ 0.74	$ 0.7
Subsequent Event [Member]
Share Price (in dollars per share)							$ 48.75
Subsequent Event [Member] \| Eastern Michigan Financial Corporation [Member]
Business Combination, Acquiree's Common Stock Conversion to Cash Ratio (in dollars per share)	$ 32.32
Business Combination, Acquiree's Common Stock Conversion to Acquire's Common Stock Ratio	0.7116
Business Combination, Consideration Transferred \| $	$ 95.8
Subsequent Event [Member] \| O 2025 Q3 Dividends [Member]
Common Stock, Dividends, Per Share, Cash Paid (in dollars per share)		$ 0.38
Dividends Payable, Date Declared		Jul. 17, 2025
Dividends Payable, Date to be Paid		Sep. 17, 2025
Dividends Payable, Date of Record		Sep. 05, 2025