Number of financing receivables that are in the process of foreclosure.

No definition available.

Name:	mbin_MortgageLoansInProcessOfForeclosureNumberOfContracts
Namespace Prefix:	mbin_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of residential loans in process of foreclosure.

+ References

No definition available.

+ Details

Name:	mbin_ResidentialLoansInProcessOfForeclosure
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Loan Losses - Troubled Debt and Modifications (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 item	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 item	Dec. 31, 2018 USD ($)
Troubled debt and modifications
Number of troubled debt restructuring \| item	0	0	0	0
Number of loans restructured during the last twelve months that defaulted during the period \| item	0	0	0	0
Residential real estate
Troubled debt and modifications
Number of loans in the process of foreclosure \| $					0
Value of residential loans in process of foreclosure \| $	$ 725,000		$ 725,000