The amount of the portfolio of loans sold in a securitization transaction.

No definition available.

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

- Definition

Number of financing receivables that are in the process of foreclosure as of the end of the reporting period..

+ References

No definition available.

+ Details

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

- Definition

Represents the mortgage servicing right established.

+ References

No definition available.

+ Details

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

- Definition

The number of loans securitized during the period.

+ References

No definition available.

+ Details

Name:	mbin_NumberOfLoansSecuritized
Namespace Prefix:	mbin_
Data Type:	xbrli:integerItemType
Balance Type:	na
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_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans and leases that were sold during the reporting period. This element refers to the gain (loss) and not to the cash proceeds of the sales. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

+ Details

Name:	us-gaap_GainLossOnSaleOfLoansAndLeases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow associated with purchasing loans held for investment purposes during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-13

+ Details

Name:	us-gaap_PaymentsToAcquireLoansHeldForInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=mbin_LoanSaleAndFreddieMacQSeriesSecuritizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Loans and Allowance for Credit Losses on Loans - Narrative (Details) $ in Thousands		9 Months Ended
	Aug. 31, 2023 USD ($) loan	Sep. 30, 2023 USD ($) loan	Sep. 30, 2022 USD ($)	Dec. 31, 2022 loan
Loans and Allowance for Credit Losses on Loans
Purchase of loans		$ 329,014	$ 289,030
Multi-family financing \| Loan Sale and Freddie Mac Q Series Securitization
Loans and Allowance for Credit Losses on Loans
Amount of portfolio of loans sold in a securitization transaction	$ 303,600
Number of loans securitized \| loan	11
Loss on sale of loans	$ 60,000
Mortgage servicing right established	$ 1,500
Residential real estate
Loans and Allowance for Credit Losses on Loans
Number of loans in the process of foreclosure \| loan		0		0