Represents financing receivable modifications specific reserve.

No definition available.

Name:	mcb_FinancingReceivableModificationsSpecificReserve
Namespace Prefix:	mcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

+ Details

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

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
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_LoansAndLeasesReceivableDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mcb_OneToFourFamilyRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

LOANS AND ALLOWANCE FOR LOAN LOSSES (Troubled Debt Restructurings) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 loan	Sep. 30, 2021 USD ($) item loan	Sep. 30, 2020 loan item	Dec. 31, 2020 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	$ 1,307		$ 1,307		$ 1,360
Number of TDR loans during the period \| loan	0	0	0	0
Specific reserves modified as TDRs	$ 33,000		$ 33,000		53,000
Number of contracts financing receivable modifications \| item			0	0
Real estate \| Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	349		$ 349		361
Real estate \| One to four family
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	$ 958		$ 958		$ 999