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Note 17 - Regulatory Capital (Details Textual)	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2019
Capital Conservation Buffer Phase in Amount	0.625%
Capital Conservation Buffer Phase-in Number of Years	4 years
Scenario, Forecast [Member]
Capital Conservation Buffer Maximum Percentage		2.50%

X

- 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

X

- 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

X

- 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

X

- Details

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