Note 18 - Fair Value Disclosure Measurements (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Estimated Selling Costs of Impaired Loans	$ 2,100,000	$ 492,000

The estimated amount of selling costs that would incur when impaired loans sold.

No definition available.

Name:	mbcn_EstimatedSellingCostsOfImpairedLoans
Namespace Prefix:	mbcn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration