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

Amount of financing receivable earlier modified by troubled debt restructuring and subsequently revert back to prepayment status due to application of COVID-19 and CARES Act.

+ References

No definition available.

+ Details

Name:	mcb_FinancingReceivableTroubledDebtRestructuringReturnedToPrepaymentSubsequentCovid19AndCaresAct
Namespace Prefix:	mcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of financing receivables that have been earlier modified by troubled debt restructuring and subsequently revert back to prepayment status due to application of COVID-19 and CARES Act.

+ References

No definition available.

+ Details

Name:	mcb_FinancingReceivableTroubledDebtRestructuringReturnedToPrepaymentSubsequentCovid19AndCaresActNumberOfContracts
Namespace Prefix:	mcb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- 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=118936363&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=118939409&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=118936363&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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mcb_OneToFourFamilyRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mcb_Covid19ImpactMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

LOANS AND ALLOWANCE FOR LOAN LOSSES (Troubled Debt Restructurings) (Details)	3 Months Ended	6 Months Ended		7 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($) item loan	Jun. 30, 2019 item	Jul. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	$ 1,393,000	$ 1,393,000			$ 1,441,000
Number of TDR loans during the period	0	0			0
Specific reserves modified as TDRs	$ 65,000	$ 65,000			$ 81,000
Number of contracts financing receivable modifications \| item		0	0
One to four family
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	1,016,000	$ 1,016,000			1,039,000
COVID 19 - Impact
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	527,600,000	$ 527,600,000
Number of TDR loans during the period \| loan		300
Number of modified loans returned to prepayment status \| loan				116
Amount of modified loans returned to prepayment status				$ 91,000,000.0
Real estate \| Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	363,000	$ 363,000			367,000
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans modified in troubled debt restructurings	$ 14,000	$ 14,000			$ 35,000