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Note 11 - Federal Income Taxes (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Jun. 01, 2014
Note 11 - Federal Income Taxes (Details) [Line Items]      
Deferred Tax Assets, Valuation Allowance $ 450,000us-gaap_DeferredTaxAssetsValuationAllowance $ 0us-gaap_DeferredTaxAssetsValuationAllowance  
Federal Alternative Minimum Tax Credits 2,800,000mbwm_FederalAlternativeMinimumTaxCredits    
Losses on Capital Investments Acquired [Member]      
Note 11 - Federal Income Taxes (Details) [Line Items]      
Deferred Tax Assets, Valuation Allowance     500,000us-gaap_DeferredTaxAssetsValuationAllowance
/ us-gaap_ValuationAllowanceByDeferredTaxAssetAxis
= mbwm_LossesOnCapitalInvestmentsAcquiredMember
General Business Tax Credit Carryforward [Member]      
Note 11 - Federal Income Taxes (Details) [Line Items]      
Tax Credit Carryforward, Amount $ 600,000us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_GeneralBusinessMember