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Note 5 - Fair Value Measurements - Assets Measured on a Nonrecurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Collateral-dependent loans | $ 4,155 | $ 3,361
Fair Value, Inputs, Level 1 [Member] |  |
Collateral-dependent loans | 0 | 0
Fair Value, Inputs, Level 2 [Member] |  |
Collateral-dependent loans | 0 | 0
Fair Value, Inputs, Level 3 [Member] |  |
Collateral-dependent loans | $ 4,155 | $ 3,361

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- Definition Fair value of impaired loans receivable. + 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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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |