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Note 3 - Loans and Allowance for Loan Losses (Details) - Nonperforming Loans (USD $) | Mar. 31, 2014 | Dec. 31, 2013
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Nonperforming Loans [Abstract] |  |
Loans past due 90 days or more still accruing interest | $ 0 | $ 0
Nonaccrual loans | 6,342,000 | 6,718,000
Total nonperforming loans | $ 6,342,000 | $ 6,718,000

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- Definition Financing receivable past due ninety days or more and still accruing interest and nonaccrual loans and troubled debt restructurings accruing interest net. + References No definition available. + Details
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Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Recorded investment in financing receivables that are 90 days or more past due and still accruing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5111-111524 + Details
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Balance Type: | debit
Period Type: | instant

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- Definition Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5111-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
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Period Type: | instant