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Note 18 - Fair Value Measurements - Additional Quantitative Information About Assets Measured at Fair Value on Non-recurring Basis (Details) - Fair Value, Measurements, Nonrecurring [Member] - Fair Value, Inputs, Level 3 [Member] - Appraisal of Collateral [Member] $ in Thousands | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
--- | --- | ---
Impaired loans, fair value estimate | [1] | $ 1,075 | $ 3,072
Other real estate owned, fair value estimate | [1] |  | $ 32
Minimum [Member] | Measurement Input, Discount Rate [Member] |  |  |
Impaired loans, discount rate | [2] | 0 | 0
Other real estate owned, discount rate | [2] |  | 0
Maximum [Member] | Measurement Input, Discount Rate [Member] |  |  |
Impaired loans, discount rate | [2] | 1 | 0.861
Other real estate owned, discount rate | [2] |  | 0.1
Weighted Average [Member] | Measurement Input, Discount Rate [Member] |  |  |
Impaired loans, discount rate | [2] | (0.406) | 0.138
[1] | Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various level III inputs which are not identifiable, less any associated allowance.
[2] | Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated liquidation expenses. The range and weighted average of liquidation expenses and other appraisal adjustments are presented as a percent of the appraisal.

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- Definition Fair value portion of impaired loans. + References No definition available. + Details
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Namespace Prefix: | mbcn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Value of input used to measure impaired loans. + References No definition available. + Details
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- Definition Fair value portion of other real estate and foreclosed assets. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Details
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- Details
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- Details
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- Details
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- Details
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