Note 5 - Fair Value Measurements - Estimated Fair Value of the Company's Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Reported Value Measurement [Member]
Financial assets:
Cash and cash equivalents	$ 120,025	$ 107,933
Loans held for sale	791	597
Net loans	992,281	984,681
Bank-owned life insurance	16,403	16,080
Federal Home Loan Bank stock	3,848	3,679
Accrued interest receivable	3,684	3,633
Financial liabilities:
Deposits	1,034,413	1,016,067
Short-term borrowings	92,000	90,398
Other borrowings	12,359	8,803
Accrued interest payable	1,020	744
Estimate of Fair Value Measurement [Member]
Financial assets:
Cash and cash equivalents	120,025	107,933
Loans held for sale	791	597
Net loans	988,336	973,124
Bank-owned life insurance	16,403	16,080
Federal Home Loan Bank stock	3,848	3,679
Accrued interest receivable	3,684	3,633
Financial liabilities:
Deposits	1,036,760	1,014,044
Short-term borrowings	92,000	90,398
Other borrowings	12,405	8,827
Accrued interest payable	1,020	744
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents	120,025	107,933
Loans held for sale
Net loans
Bank-owned life insurance	16,403	16,080
Federal Home Loan Bank stock	3,848	3,679
Accrued interest receivable	3,684	3,633
Financial liabilities:
Deposits	643,692	715,153
Short-term borrowings	92,000	90,398
Other borrowings
Accrued interest payable	1,020	744
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial assets:
Cash and cash equivalents
Loans held for sale	791	597
Net loans
Bank-owned life insurance
Federal Home Loan Bank stock
Accrued interest receivable
Financial liabilities:
Deposits
Short-term borrowings
Other borrowings
Accrued interest payable
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Financial assets:
Cash and cash equivalents
Loans held for sale
Net loans	988,336	973,124
Bank-owned life insurance
Federal Home Loan Bank stock
Accrued interest receivable
Financial liabilities:
Deposits	393,068	298,891
Short-term borrowings
Other borrowings	12,405	8,827
Accrued interest payable

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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Data Type:	xbrli:monetaryItemType
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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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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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Data Type:	xbrli:monetaryItemType
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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- Details

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