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Note 10 - Commitments and Contingencies (Details Textual) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Deposits, Total | $ 1,200,557 | $ 1,225,200
Cannabis Customers [Member] |  |
Deposits, Total | $ 16,400 | $ 11,800
Deposits, Percent of Total | 1.40% | 1.00%

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- Definition The percent of total deposits of certain deposit customers/categories. + References No definition available. + Details
Name: | mbcn_DepositsPercentOfTotal
Namespace Prefix: | mbcn_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.12) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
Name: | us-gaap_Deposits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | srt_CounterpartyNameAxis=mbcn_CannabisCustomersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |