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Note 9 - Commitments and Off-balance-sheet Risk (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Note 9 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Reserve or Liability Balance for Financial Instruments with Off-balance Sheet Risk	0mbwm_ReserveOrLiabilityBalanceForFinancialInstrumentsWithOffBalanceSheetRisk	$ 0mbwm_ReserveOrLiabilityBalanceForFinancialInstrumentsWithOffBalanceSheetRisk
Minimum [Member]
Note 9 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Fees Accreted Into Income During Interest Rate Swap Agreements, Term	4 years
Maximum [Member]
Note 9 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Fees Accreted Into Income During Interest Rate Swap Agreements, Term	15 years
Interest Rate Swap [Member]
Note 9 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Derivative, Notional Amount	15,200,000invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember
Derivative, Fair Value, Net	(2,700,000)us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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X

- Definition

Period of time between issuance and maturity of interest rate swap agreements, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

The carrying amount for the reserve or liability for financial instruments with off-balance sheet risk.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbwm_
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X

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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