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Note 21 - Regulatory Matters (Details) (USD $)	0 Months Ended					12 Months Ended	0 Months Ended
	Dec. 24, 2014	Sep. 24, 2014	Jun. 25, 2014	May 29, 2014	Mar. 10, 2014	Dec. 31, 2014	Jan. 15, 2015	Dec. 31, 2013	Dec. 31, 2009	Jan. 30, 2015
Note 21 - Regulatory Matters (Details) [Line Items]
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval						$ 87,700,000us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval
Common Stock, Dividends, Per Share, Cash Paid (in Dollars per share)	$ 0.12us-gaap_CommonStockDividendsPerShareCashPaid	$ 0.12us-gaap_CommonStockDividendsPerShareCashPaid	$ 0.12us-gaap_CommonStockDividendsPerShareCashPaid	$ 2.00us-gaap_CommonStockDividendsPerShareCashPaid	$ 0.12us-gaap_CommonStockDividendsPerShareCashPaid
Trust Preferred Securities Included in Tier One Capital						52,400,000mbwm_TrustPreferredSecuritiesIncludedInTierOneCapital		32,000,000mbwm_TrustPreferredSecuritiesIncludedInTierOneCapital
Maximum Restricted Core Element Allowed in Tier One Capital, Percent						25.00%mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent
Maximum Level of Consolidated Aggregate Assets Allowing for Inclusion of Trust Preferred Securities in Tier One Capital									15,000,000,000mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOneCapital
Preferred Securities of Subsidiary Trust						52,400,000mbwm_PreferredSecuritiesOfSubsidiaryTrust		32,000,000mbwm_PreferredSecuritiesOfSubsidiaryTrust
Subsequent Event [Member]
Note 21 - Regulatory Matters (Details) [Line Items]
Common Stock, Dividends, Per Share, Declared (in Dollars per share)							$ 0.14us-gaap_CommonStockDividendsPerShareDeclared / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Stock Repurchase Program, Authorized Amount										$ 20,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1 / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember

X

- Definition

The maximum level of consolidated aggregate assets allowing for inclusion of trust preferred securities in Tier 1 Capital under the Dodd-Frank Act.

+ References

No definition available.

+ Details

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X

- Definition

The maximum amount of restricted core elements allowed in tier one capital expressed as a percent.

+ References

No definition available.

+ Details

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- Details

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- Definition

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

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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X

- Definition

Trust preferred securities held by the trust that are included in Tier One Capital and subject to certain limitations.

+ References

No definition available.

+ Details

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X

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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X

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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- Definition

Amount of dividends that can be declared or paid without approval of regulatory agency.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(e))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph e

-Article 4

+ Details

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X

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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