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Deposits (Details Textual) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Deposits (Textual) [Abstract]
Total deposits	$ 1,061,315,000	$ 1,135,204,000
Amount of decrease in total deposits	$ 73,900,000
Percentage of decrease in total deposits	6.50%

X

- Definition

Change in deposit liabilities.

+ References

No definition available.

+ Details

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X

- Details

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X

- Definition

Percentage of decrease in aggregate deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbwm_
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X

- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.12)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 9

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