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Note 10 - Hedging Activities (Details) (USD $) | 1 Months Ended |  |
--- | --- | --- | ---
Feb. 29, 2012 | Mar. 31, 2015 | Dec. 31, 2014
Note 10 - Hedging Activities (Details) [Line Items] |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust | $ 32,000,000 us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust | $ 54,642,000 us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust | $ 54,472,000 us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust
Fair Value of Interest Rate Swap Agreement Liability |  | 500,000 mbwm_FairValueOfInterestRateSwapAgreementLiability | 300,000 mbwm_FairValueOfInterestRateSwapAgreementLiability
London Interbank Offered Rate (LIBOR) [Member] | Junior Subordinated Debt [Member] |  |  |
Note 10 - 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 | $ 32,000,000 invest_DerivativeNotionalAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_JuniorSubordinatedDebtMember / us-gaap_VariableRateAxis = us-gaap_LondonInterbankOfferedRateLIBORMember |  |

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- 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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- Definition Fair value disclosure of the liability related to a derivative interest rate swap agreement. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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Period Type: | instant

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- Details
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- 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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- 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 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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- Details
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