The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=118939070&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- 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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=mcb_MultifamilyRealEstateMember
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:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
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:

- Details

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

LOANS AND ALLOWANCE FOR LOAN LOSSES (Schedule of Loans by Impairment Method) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Individually evaluated for impairment, Allowance for loan losses			$ 1,180
Collectively evaluated for impairment, Allowance for loan losses			25,092
Total ending allowance balance	$ 32,505		26,272	$ 22,715	$ 20,834	$ 18,942
Individually evaluated for impairment, Loans			5,526
Collectively evaluated for impairment, Loans			2,672,393
Total ending loan balance	2,897,292		2,677,919
COVID 19 - Impact
Loans and Leases Receivable Disclosure [Line Items]
Individually evaluated for impairment, Allowance for loan losses	1,993
Collectively evaluated for impairment, Allowance for loan losses	30,512
Total ending allowance balance	32,505	$ 27,868
Individually evaluated for impairment, Loans	9,787
Collectively evaluated for impairment, Loans	2,887,505
Total ending loan balance	2,897,292
Real estate
Loans and Leases Receivable Disclosure [Line Items]
Total ending loan balance	2,396,810		2,157,344
Real estate \| Commercial
Loans and Leases Receivable Disclosure [Line Items]
Collectively evaluated for impairment, Allowance for loan losses	18,690		15,317
Total ending allowance balance	18,690	15,891	15,317	13,006	10,885	9,037
Individually evaluated for impairment, Loans	363		367
Collectively evaluated for impairment, Loans	1,875,401		1,667,869
Total ending loan balance	1,875,764		1,668,236
Real estate \| Construction
Loans and Leases Receivable Disclosure [Line Items]
Collectively evaluated for impairment, Allowance for loan losses	741		411
Total ending allowance balance	741	549	411	501	647	625
Collectively evaluated for impairment, Loans	59,378		30,827
Total ending loan balance	59,378		30,827
Real estate \| Multi-family
Loans and Leases Receivable Disclosure [Line Items]
Collectively evaluated for impairment, Allowance for loan losses	2,739		2,453
Total ending allowance balance	2,739	2,518	2,453	2,249	2,111	2,047
Collectively evaluated for impairment, Loans	393,342		375,611
Total ending loan balance	393,342		375,611
Real estate \| One to four family
Loans and Leases Receivable Disclosure [Line Items]
Individually evaluated for impairment, Allowance for loan losses	58		64
Collectively evaluated for impairment, Allowance for loan losses	184		203
Total ending allowance balance	242	191	267	253	308	228
Individually evaluated for impairment, Loans	1,016		3,384
Collectively evaluated for impairment, Loans	67,310		79,286
Total ending loan balance	68,326		82,670
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total ending loan balance	444,265		448,619
Commercial and industrial \| Commercial
Loans and Leases Receivable Disclosure [Line Items]
Individually evaluated for impairment, Allowance for loan losses	1,408		805
Collectively evaluated for impairment, Allowance for loan losses	7,724		6,265
Total ending allowance balance	9,132	8,213	7,070	6,142	6,177	6,257
Individually evaluated for impairment, Loans	6,482		1,047
Collectively evaluated for impairment, Loans	437,783		447,572
Total ending loan balance	444,265		448,619
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total ending loan balance	56,217		71,956
Consumer \| Consumer
Loans and Leases Receivable Disclosure [Line Items]
Individually evaluated for impairment, Allowance for loan losses	527		311
Collectively evaluated for impairment, Allowance for loan losses	434		443
Total ending allowance balance	961	$ 506	754	$ 564	$ 706	$ 748
Individually evaluated for impairment, Loans	1,926		728
Collectively evaluated for impairment, Loans	54,291		71,228
Total ending loan balance	$ 56,217		$ 71,956