Consolidated Statements of Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Consolidated Statements of Income
Reclassifications included in gains on sale of investment available for sale	$ 0	$ 127
Provision for income taxes related to income tax expense for reclassification items	$ 0	$ 32

The amount related to accumulated other comprehensive earnings reclassifications included in the total gain (loss) on sale of investments.

No definition available.

Name:	mbin_GainLossOnSaleOfAvailableForSaleInvestmentsAmountRelatedToAociReclassification
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration