Share-Based Payment Plans - ESOP (Details) - ESOP - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Employee Stock Ownership Plan
Expense recognized for the contribution to the plan	$ 0	$ 0	$ 810,000	$ 653,000
Shares contributed to the plan			33,293	20,709

The amount of plan compensation cost recognized during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480489/718-40-50-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480489/718-40-50-1

+ Details

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

- Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis=mbin_EmployeeStockOwnershipPlan2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: