Note 14 - Commitments and Off-balance-sheet Risk (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Note 14 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Reserve or Liability Balance for Financial Instruments with Off-balance Sheet Risk	$ 0	$ 0
Mortgage Loans on Real Estate, Minimum Interest Rate in Range	4.00%
Mortgage Loans on Real Estate, Maximum Interest Rate in Range	7.00%
Term Debt Secured by Real Estate Balloon Payment Period	5 years
Term Debt Secured by Non-Real Estate Collateral Maturity Period	5 years
Liabilities for Accreted Fee Collected from Customer	100,000	100,000
Amount of Federal Reserve Requirement	8,400,000mbwm_AmountOfFederalReserveRequirement	1,500,000mbwm_AmountOfFederalReserveRequirement
Interest Rate Swap [Member]
Note 14 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Derivative, Notional Amount	15,400,000
Derivative, Fair Value, Net	$ (2,900,000)
Minimum [Member]
Note 14 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Amortization Period for Term Debt Secured by Real Estate	10 years
Interest Rates on Loans Secured by Non-Real Estate Collateral	4.00%
Fees Accreted Into Income During Interest Rate Swap Agreements Term	4 years
Maximum [Member]
Note 14 - Commitments and Off-balance-sheet Risk (Details) [Line Items]
Amortization Period for Term Debt Secured by Real Estate	20 years
Interest Rates on Loans Secured by Non-Real Estate Collateral	7.50%
Fees Accreted Into Income During Interest Rate Swap Agreements Term	15 years

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

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

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Amortization period for term debt secured by real estate.

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- Definition

Amount of federal reserve requirement at period end that can be met with vault cash or deposits at a Federal Reserve Bank.

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- Definition

The fees associated with an interest rate swap agreement that have been accreted.

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- Definition

Interest rates on loans secured by non-real estate collateral.

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- Definition

Liabilities for accreted fee collected from customer.

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- Definition

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

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- Definition

Term debt secured by non-real estate collateral maturity period.

+ References

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- Definition

Term debt secured by real estate balloon payment period.

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- 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=35750535&loc=d3e13433-108611

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-Name Accounting Standards Codification

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-Section 45

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

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-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

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-Paragraph 6

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

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- Definition

The highest stated interest rate within the mortgage loans included in the loan grouping.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher FASB

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-Subparagraph (SX 210.12-29.3)

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 29

-Article 12

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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The lowest stated interest rate within the mortgage loans included in the loan grouping.

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