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Note 13 - Regulatory Matters (Details) (USD $) | 0 Months Ended | 3 Months Ended | 0 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 25, 2015 | Mar. 31, 2015 | Mar. 31, 2014 | Apr. 16, 2015 | Jan. 30, 2015 | Dec. 31, 2014 | Dec. 31, 2009
Note 13 - Regulatory Matters (Details) [Line Items] |  |  |  |  |  |  |
Trust Preferred Securities Included in Tier One Capital |  | $ 52,600,000 mbwm_TrustPreferredSecuritiesIncludedInTierOneCapital |  |  |  | $ 52,400,000 mbwm_TrustPreferredSecuritiesIncludedInTierOneCapital |
Maximum Restricted Core Element Allowed in Tier One Capital, Percent |  | 25.00%mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent |  |  |  |  |
Maximum Level of Consolidated Aggregate Assets Allowing for Inclusion of Trust Preferred Securities in Tier One Capital |  |  |  |  |  |  | 15,000,000,000 mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOneCapital
Preferred Securities of Subsidiary Trust |  | 52,600,000 mbwm_PreferredSecuritiesOfSubsidiaryTrust |  |  |  | 52,400,000 mbwm_PreferredSecuritiesOfSubsidiaryTrust |
Common Stock, Dividends, Per Share, Cash Paid (in Dollars per share) | $ 0.14 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.14 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.12 us-gaap_CommonStockDividendsPerShareCashPaid |  |  |  |
Stock Repurchase Program, Authorized Amount |  |  |  |  | 20,000,000 us-gaap_StockRepurchaseProgramAuthorizedAmount1 |  |
Subsequent Event [Member] |  |  |  |  |  |  |
Note 13 - Regulatory Matters (Details) [Line Items] |  |  |  |  |  |  |
Common Stock, Dividends, Per Share, Declared (in Dollars per share) |  |  |  | $ 0.14 us-gaap_CommonStockDividendsPerShareDeclared / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |
Repurchased Stock [Member] |  |  |  |  |  |  |
Note 13 - Regulatory Matters (Details) [Line Items] |  |  |  |  |  |  |
Stock Repurchased During Period, Shares (in Shares) |  | 104,000 us-gaap_StockRepurchasedDuringPeriodShares / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_RepurchasedStockMember |  |  |  |  |
Share Price (in Dollars per share) |  | $ 19.09 us-gaap_SharePrice / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_RepurchasedStockMember |  |  |  |  |
Stock Repurchased During Period, Value |  | $ 2,000,000 us-gaap_StockRepurchasedDuringPeriodValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mbwm_RepurchasedStockMember |  |  |  |  |

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- Definition The maximum level of consolidated aggregate assets allowing for inclusion of trust preferred securities in Tier 1 Capital under the Dodd-Frank Act. + References No definition available. + Details
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- Definition The maximum amount of restricted core elements allowed in tier one capital expressed as a percent. + References No definition available. + Details
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- Definition Trust preferred securities possesses characteristics of both equity and debt issues and are generally issued by bank holding companies. + References No definition available. + Details
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- Definition Trust preferred securities held by the trust that are included in Tier One Capital and subject to certain limitations. + References No definition available. + Details
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- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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- Definition Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 + Details
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