Note 5 - Fair Value Measurements - Estimated Fair Value of the Company's Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Reported Value Measurement [Member]
Financial assets:
Cash and cash equivalents	$ 52,981	$ 35,113
Loans held for sale	10,457	1,220
Net loans	1,113,037	977,490
Bank-owned life insurance	16,832	16,511
Federal Home Loan Bank stock	5,207	3,848
Accrued interest receivable	5,998	3,471
Financial liabilities:
Deposits	1,193,963	1,020,843
Short-term borrowings	0	5,075
Other borrowings	17,100	12,750
Accrued interest payable	788	917
Estimate of Fair Value Measurement [Member]
Financial assets:
Cash and cash equivalents	52,981	35,113
Loans held for sale	10,457	1,220
Net loans	1,113,962	974,213
Bank-owned life insurance	16,832	16,511
Federal Home Loan Bank stock	5,207	3,848
Accrued interest receivable	5,998	3,471
Financial liabilities:
Deposits	1,198,722	1,023,236
Short-term borrowings	0	5,075
Other borrowings	13,149	12,783
Accrued interest payable	788	917
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents	52,981	35,113
Loans held for sale	0	0
Net loans	0	0
Bank-owned life insurance	16,832	16,511
Federal Home Loan Bank stock	5,207	3,848
Accrued interest receivable	5,998	3,471
Financial liabilities:
Deposits	864,550	652,043
Short-term borrowings	0	5,075
Other borrowings	0	0
Accrued interest payable	788	917
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial assets:
Cash and cash equivalents	0	0
Loans held for sale	10,457	1,220
Net loans	0	0
Bank-owned life insurance	0	0
Federal Home Loan Bank stock	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Short-term borrowings	0	0
Other borrowings	0	0
Accrued interest payable	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Financial assets:
Cash and cash equivalents	0	0
Loans held for sale	0	0
Net loans	1,113,962	974,213
Bank-owned life insurance	0	0
Federal Home Loan Bank stock	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	334,172	371,193
Short-term borrowings	0	0
Other borrowings	13,149	12,783
Accrued interest payable	$ 0	$ 0

Fair value portion of accrued interest payable.

No definition available.

Name:	mbcn_AccruedInterestPayableFairValueDisclosure
Namespace Prefix:	mbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value portion of a life insurance policy on an officer, executive or employee for which the reporting entity (a bank) is entitled to proceeds from the policy upon death of the insured or surrender of the insurance policy.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

The fair value portion as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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Period Type:	instant

- References

No definition available.

+ Details

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Period Type:	duration

- References

No definition available.

+ Details

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Period Type:	duration

- Definition

Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

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Balance Type:	debit
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- Definition

Fair value portion of other liabilities.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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- Details

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