Note 7 - Investment and Equity Securities - Equity Investments Without Readily Determinable Fair Values (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($)
Amortized cost, annual	$ 232
Amortized cost, cumulative	232
Impairment, annual
Impairment, cumulative
Observable price changes, annual	18
Observable price changes, cumulative	18
Carrying value, annual	250
Carrying value, cumulative	$ 250

Annual amortized cost of investment in equity security without readily determinable fair value.

No definition available.

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- Definition

Cumulative amortized cost of investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbcn_
Data Type:	xbrli:monetaryItemType
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- Definition

Annual amount from observable price change in investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbcn_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Cumulative amount from observable price change in investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

+ Details

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- Definition

Amount of impairment loss on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Amount of cumulative impairment loss on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

+ Details

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