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Note 3 - Investment Securities Available For Sale (Details) (USD $) | Dec. 31, 2014 | Dec. 31, 2013
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Investments, Debt and Equity Securities [Abstract] |  |
Available-for-sale Securities Pledged as Collateral | $ 61,900,000 us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral | $ 66,300,000 us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | 66 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 |
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held | $ 0 us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld |
Percentage of Portfolio | 97.60%mbcn_PercentageOfPortfolio |

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- Definition Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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- Definition The fair value of available-for-sale securities that serve as collateral for borrowings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5086-111524 + Details
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- Definition The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27340-111563 + Details
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