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Deposits (Details Textual) (USD $) | 6 Months Ended |
--- | --- | ---
Jun. 30, 2012 | Dec. 31, 2011
Deposits (Textual) [Abstract] |  |
Total deposits | $ 1,105,630,000 | $ 1,112,075,000
Amount of decrease in total deposits | $ 6,400,000 |
Percentage of decrease in total deposits | 0.60% |

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- Definition Change in deposit liabilities. + References No definition available. + Details
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Balance Type: | credit
Period Type: | duration

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

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- Definition Percentage of decrease in aggregate deposits. + References No definition available. + Details
Name: | mbwm_PercentageOfDecreaseInAggregateDeposits
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- 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 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Paragraph 37, 38, 39 -IssueDate 2006-05-01 -Chapter 13 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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Balance Type: | credit
Period Type: | instant