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Note 5 - Fair Value Measurements - Additional Quantitative Information About Assets Measured at Fair Value on Non-recurring Basis (Details) - Fair Value, Nonrecurring [Member] $ in Thousands | Sep. 30, 2025 USD ($) | Dec. 31, 2024 USD ($)
--- | --- | ---
Collateral-dependent loans | $ 6,007 | $ 3,321 |
Premises and equipment held for sale | 998 |  |
Fair Value, Inputs, Level 3 [Member] |  |  |
Collateral-dependent loans | 6,007 | 3,321 |
Premises and equipment held for sale | 998 |  |
Appraisal of Collateral [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Collateral-dependent loans | $ 6,007 | $ 3,321 |
Appraisal of Collateral [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Appraised Value [Member] | Minimum [Member] |  |  |
Collateral-dependent loans, range | 0.128 | 0 | [1]
Appraisal of Collateral [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Appraised Value [Member] | Maximum [Member] |  |  |
Collateral-dependent loans, range | 0.292 | 0.239 | [2]
Appraisal of Collateral [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Appraised Value [Member] | Weighted Average [Member] |  |  |
Collateral-dependent loans, range | 0.252 | 0.239 |
Sale Price [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Premises and equipment held for sale | $ 998 |  |
Sale Price [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Adjustments to Selling Price [Member] | Weighted Average [Member] |  |  |
Premises and equipment held for sale, rang | 0.05 |  |
[1] | Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various level III inputs that 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 Value of input used to measure impaired loans. + References No definition available. + Details
Name: | mbcn_ImpairedLoansMeasurementInput
Namespace Prefix: | mbcn_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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

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- Definition The fair value of the property plant and equipment held for sale. + References No definition available. + Details
Name: | mbcn_PropertyPlantAndEquipmentHeldForSaleFairValue
Namespace Prefix: | mbcn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The measurement input for the property, plant and equipment held for sale. + References No definition available. + Details
Name: | mbcn_PropertyPlantAndEquipmentHeldForSaleMeasurementInput
Namespace Prefix: | mbcn_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ValuationTechniqueAxis=mbcn_AppraisalOfCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputAppraisedValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ValuationTechniqueAxis=mbcn_SalePriceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_MeasurementInputTypeAxis=mbcn_MeasurementInputAdjustmentsToSellingPriceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |