Loans and Allowance for Loan Losses (Details 2) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Nonperforming loans
Loans past due 90 days or more still accruing interest	$ 0	$ 0
Nonaccrual loans, including troubled debt restructurings	18,970,000	45,074,000
Troubled debt restructurings, accruing interest included in total nonperforming loans	0	0
Total nonperforming loans	$ 18,970,000	$ 45,074,000

Financing receivable past due ninety days or more and still accruing interest and nonaccrual loans and troubled debt restructurings accruing interest net.

No definition available.

+ Details

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Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	mbwm_NonperformingLoansAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6951948&loc=d3e18845-111554

+ Details

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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=7512638&loc=d3e5111-111524

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant