Note 5 - Fair Value Measurements (Details Textual) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Estimated Selling Costs of Impaired Loans	$ 2.0	$ 2.1

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