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Note 22 - U.S. Treasury Capital Purchase Program Participation (Details) (USD $)
 0 Months Ended 3 Months Ended 12 Months Ended
May 15, 2009
Sep. 30, 2012
Jun. 30, 2012
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Note 22 - U.S. Treasury Capital Purchase Program Participation (Details) [Line Items]            
Proceeds from Issuance or Sale of Equity $ 21,000,000us-gaap_ProceedsFromIssuanceOrSaleOfEquity          
Number of Cumulative Perpetual Preferred Shares Received by Treasury under Capital Purchase Program (in Shares) 21,000mbwm_NumberOfCumulativePerpetualPreferredSharesReceivedByTreasuryUnderCapitalPurchaseProgram          
Preferred Stock, Redemption Price Per Share (in Dollars per share) $ 1,000us-gaap_PreferredStockRedemptionPricePerShare          
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in Shares) 616,438us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights          
Preferred Stock, Par or Stated Value Per Share (in Dollars per share) $ 0us-gaap_PreferredStockParOrStatedValuePerShare     $ 0us-gaap_PreferredStockParOrStatedValuePerShare $ 0us-gaap_PreferredStockParOrStatedValuePerShare  
Cumulative Dividends Preferred Stock Dividend Rate Percentage for First Five Years 5.00%mbwm_CumulativeDividendsPreferredStockDividendRatePercentageForFirstFiveYears          
Cumulative Dividends Preferred Stock Dividend Rate Percentage for After Five Years 9.00%mbwm_CumulativeDividendsPreferredStockDividendRatePercentageForAfterFiveYears          
Warrant Expiration Period 10 years          
Class of Warrant or Right, Exercise Price of Warrants or Rights (in Dollars per share) $ 5.11us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1          
Reduction from Retained Earnings Resulting from Accelerated Discount on Preferred Stock     600,000mbwm_ReductionFromRetainedEarningsResultingFromAcceleratedDiscountOnPreferredStock      
Amortization Period for Accelerated Discount on Preferred Stock     5 years      
Payments for Repurchase of Warrants   7,500,000us-gaap_PaymentsForRepurchaseOfWarrants   0us-gaap_PaymentsForRepurchaseOfWarrants 0us-gaap_PaymentsForRepurchaseOfWarrants 7,465,000us-gaap_PaymentsForRepurchaseOfWarrants
Reduction in Shareholders' Equity Resulting from Repurchase of Warrant   7,500,000mbwm_ReductionInShareholdersEquityResultingFromRepurchaseOfWarrant        
Preferred Stock 1 [Member]            
Note 22 - U.S. Treasury Capital Purchase Program Participation (Details) [Line Items]            
Treasury Stock, Value, Acquired, Par Value Method     $ 21,000,000us-gaap_TreasuryStockValueAcquiredParValueMethod
/ us-gaap_StatementClassOfStockAxis
= mbwm_PreferredStock1Member