The amount of contingent line of credit outstanding.

No definition available.

Name:	mbin_ContingentLineOfCredit
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of non-contingent reserve on sale of loan.

+ References

No definition available.

+ Details

Name:	mbin_LoanPortfolioNonContingentReserve
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of potential obligation to repurchase the loans receivable already sold.

+ References

No definition available.

+ Details

Name:	mbin_LossContingencyObligationToRepurchaseLoansReceivablesSold
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reserve liability for risk-sharing obligation.

+ References

No definition available.

+ Details

Name:	mbin_ReserveLiabilityForRiskSharingObligation
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of additional unfunded investment obligations in debt fund joint ventures.

+ References

No definition available.

+ Details

Name:	mbin_UnfundedAdditionalInvestmentObligationsInDebtFundJointVentures
Namespace Prefix:	mbin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_FairValueOffBalanceSheetRisksDisclosureInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of commitment or contingent commitments to qualified affordable housing project investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 323
-SubTopic 740
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481543/323-740-50-2

+ Details

Name:	us-gaap_QualifiedAffordableHousingProjectInvestmentsCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
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_LossContingenciesByNatureOfContingencyAxis=us-gaap_IndemnificationGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=mbin_FannieMaeOrFreddieMacMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments, Credit Risk, and Contingencies - Other (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	May 05, 2022	Dec. 31, 2021
Commitments and Credit Risk
Reserve liability	$ 800,000	$ 500,000
Outstanding line of credit	0	0		$ 0
Additional contribution on qualified affordable housing limited partnerships	61,400,000	36,800,000
Other liabilities
Commitments and Credit Risk
Additional contribution on qualified affordable housing limited partnerships	61,400,000	36,800,000
Unfunded liability to invest in debt fund joint ventures	4,000,000.0	5,200,000
Loan Sale and Freddie Mac Q Series Securitization \| Other liabilities
Commitments and Credit Risk
Non-contingent reserve	2,500,000	2,500,000	$ 2,500,000
Loan Sale and Freddie Mac Q Series Securitization \| Indemnification agreement \| Other liabilities
Commitments and Credit Risk
Financial guarantees	1,200,000	1,200,000
Fannie Mae or Freddie Mac \| Other liabilities
Commitments and Credit Risk
Potential obligation for repurchase of loans	$ 1,000,000.0	$ 900,000