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Regulatory Capital - Additional Information (Detail) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 | Jan. 01, 2019
Capital Conservation Buffer, Phase in Amount |  |
Capital Conservation Buffer, Phase in Amount | 0.625% |
Capital Conservation Buffer, Phase-in, Number of years | 4 years |
Scenario, Forecast [Member] |  |
Capital Conservation Buffer, Phase in Amount |  |
Capital Conservation Buffer, Maximum Percentage |  | 2.50%

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- Definition The maximum percentage that the capital conservation buffer will be after the final phase-in has taken effect. + References No definition available. + Details
Name: | mbcn_CapitalConservationBufferMaximumPercentage
Namespace Prefix: | mbcn_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Percentage that the capital conservation buffer will increase by each year until the maximum amount is reached. + References No definition available. + Details
Name: | mbcn_CapitalConservationBufferPhaseInAmount
Namespace Prefix: | mbcn_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of years that the capital conservation buffer percentage will be stepped up on a per year basis. + References No definition available. + Details
Name: | mbcn_CapitalConservationBufferPhaseinNumberOfYears
Namespace Prefix: | mbcn_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Capital [Line Items] + References No definition available. + Details
Name: | mbcn_CapitalLineItems
Namespace Prefix: | mbcn_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |