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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] - Fair Value, Inputs, Level 3 [Member] - Appraisal of Collateral [Member] $ in Thousands	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Collateral-dependent loans	$ 4,155	$ 3,361
Measurement Input, Appraised Value [Member] | Minimum [Member]
Collateral-dependent loans, range	0.104	0.201
Measurement Input, Appraised Value [Member] | Maximum [Member]
Collateral-dependent loans, range	0.239

X

- 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

X

- 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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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