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Note 16 - Hedging Activities (Details) (USD $)	1 Months Ended
	Feb. 29, 2012	Dec. 31, 2014	Dec. 31, 2013
Note 16 - Hedging Activities (Details) [Line Items]
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	$ 32,000,000us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	$ 54,472,000us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	$ 32,990,000us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust
Fair Value of Interest Rate Swap Agreement Liability		300,000mbwm_FairValueOfInterestRateSwapAgreementLiability	300,000mbwm_FairValueOfInterestRateSwapAgreementLiability
Junior Subordinated Debt [Member] | London Interbank Offered Rate (LIBOR) [Member]
Note 16 - Hedging Activities (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.18%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_LongtermDebtTypeAxis = us-gaap_JuniorSubordinatedDebtMember / us-gaap_VariableRateAxis = us-gaap_LondonInterbankOfferedRateLIBORMember
Derivative, Notional Amount	$ 32,000,000invest_DerivativeNotionalAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_JuniorSubordinatedDebtMember / us-gaap_VariableRateAxis = us-gaap_LondonInterbankOfferedRateLIBORMember

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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Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The fair value of a derivative interest rate swap agreement liability.

+ References

No definition available.

+ Details

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

X

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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