Note 18 - Fair Value Measurements - Estimated Fair Value of the Company's Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Reported Value Measurement [Member]
Financial assets:
Cash and cash equivalents	$ 107,933	$ 39,886
Loans held for sale	597	463
Net loans	984,681	916,023
Bank-owned life insurance	16,080	15,652
Federal Home Loan Bank stock	3,679	3,589
Accrued interest receivable	3,633	3,288
Financial liabilities:
Deposits	1,016,067	878,194
Short-term borrowings	90,398	74,707
Other borrowings	8,803	29,065
Accrued interest payable	744	578
Estimate of Fair Value Measurement [Member]
Financial assets:
Cash and cash equivalents	107,933	39,886
Loans held for sale	597	463
Net loans	973,124	913,323
Bank-owned life insurance	16,080	15,652
Federal Home Loan Bank stock	3,679	3,589
Accrued interest receivable	3,633	3,288
Financial liabilities:
Deposits	1,014,044	877,227
Short-term borrowings	90,398	74,707
Other borrowings	8,827	29,069
Accrued interest payable	744	578
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents	107,933	39,886
Loans held for sale
Net loans
Bank-owned life insurance	16,080	15,652
Federal Home Loan Bank stock	3,679	3,589
Accrued interest receivable	3,633	3,288
Financial liabilities:
Deposits	715,153	635,207
Short-term borrowings	90,398	74,707
Other borrowings
Accrued interest payable	744	578
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial assets:
Cash and cash equivalents
Loans held for sale	597	463
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	973,124	913,323
Bank-owned life insurance
Federal Home Loan Bank stock
Accrued interest receivable
Financial liabilities:
Deposits	298,891	242,020
Short-term borrowings
Other borrowings	8,827	29,069
Accrued interest payable

Fair value portion of accrued interest payable.

No definition available.

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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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