Name:	mbwm_AmortizationOfFairValueDiscountRelatedToSubordinatedDebenturesOfAssumedBusinessTrusts
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
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Represents the amortization period of the fair value discount related to subordinated debentures of assumed business trusts.

No definition available.

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Namespace Prefix:	mbwm_
Data Type:	xbrli:durationItemType
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The number of trusts for which debt assumed in a business combination are payable to.

No definition available.

Name:	mbwm_BusinessCombinationDebtAssumedNumberOfTrusts
Namespace Prefix:	mbwm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the fair value discount of subordinated debentures related to assumed business trusts at the time of the merger.

No definition available.

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

Amount of commitment or contingent commitments to low-income housing tax credit and historic tax credit.

No definition available.

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

Amount of investment in low-income housing tax credit and historic tax credits.

No definition available.

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

Represents the Company's business trusts.

No definition available.

Name:	mbwm_NumberOfBusinessTrusts
Namespace Prefix:	mbwm_
Data Type:	xbrli:integerItemType
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Period Type:	instant

Trust preferred securities possesses characteristics of both equity and debt issues and are generally issued by bank holding companies.

No definition available.

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

Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

The cash outflow to reacquire preferred stocks issued by a business trust or other special purpose entity, mainly established by a bank holding entity, to third party investors. The trust's assets are deeply subordinated debentures of the bank holding entity. Most trust preferred securities are subject to a mandatory redemption upon the repayment of the debentures.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-15

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

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-5A

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
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Period Type:	duration

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubordinatedBorrowingAxis=mbwm_MercantileBankCapitalTrustIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_CounterpartyNameAxis=mbwm_FundMember
Namespace Prefix:
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