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Note 3 - Loans and Allowance for Loan Losses (Details) - Loans Modified as Troubled Debt Restructurings Within the Previous Twelve Months That Became Over 30 Days Past Due (USD $) | 3 Months Ended
--- | ---
Mar. 31, 2014 | Mar. 31, 2013
Commercial: |  |
Number of Contracts | 0 | 1
Recorded Principal Balance | $ 0 | $ 44,000
Commercial and Industrial [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | 0 | 0
Vacant Land,Land Developement and Residential Construction [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | 0 | 0
Real Estate-Owner Occupied [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 1
Recorded Principal Balance | 0 | 44,000
Real Estate-Non-Owner Occupied [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | 0 | 0
Real Estate-Multi Family And Residential Rental [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | 0 | 0
Commercial [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 1
Recorded Principal Balance | 0 | 44,000
Home Equity and Other [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | 0 | 0
One-Four Family Mortgages [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | 0 | 0
Retail [Member] |  |
Commercial: |  |
Number of Contracts | 0 | 0
Recorded Principal Balance | $ 0 | $ 0

X
- Details
Name: | mbwm_CommercialAbstract000000000
Namespace Prefix: | mbwm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing receivables modifications subsequent default number of contracts. + References No definition available. + Details
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Namespace Prefix: | mbwm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing receivables modifications subsequent default recorded investment. + References No definition available. + Details
Name: | mbwm_FinancingReceivablesModificationsSubsequentDefaultRecordedInvestmen
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration