FAIR VALUE - Inputs and Valuation technique (Details)	Dec. 31, 2021	Dec. 31, 2020
Obligations of U.S. Government entities and agencies
Fair value measurement inputs and valuation techniques
Valuation technique of available for sale securities	us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember
SBA servicing assets and Interest only strip
Fair value measurement inputs and valuation techniques
Valuation technique of servicing asset	us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Impaired Loans
Fair value measurement inputs and valuation techniques
Valuation technique of available for sale securities	us-gaap:ValuationTechniqueConsensusPricingModelMember	us-gaap:ValuationTechniqueConsensusPricingModelMember
Foreclosed real estate
Fair value measurement inputs and valuation techniques
Valuation technique of available for sale securities		us-gaap:ValuationTechniqueConsensusPricingModelMember
Discount Rate
Fair value measurement inputs and valuation techniques
Servicing asset measurement input	13.50	14.00
Prepayment speed
Fair value measurement inputs and valuation techniques
Servicing asset measurement input	21.79	20.71
Recurring \| Discount Rate \| Minimum \| Obligations of U.S. Government entities and agencies
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	0	0
Recurring \| Discount Rate \| Minimum \| SBA servicing assets and Interest only strip
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	7.57
Servicing asset measurement input		4.67
Recurring \| Discount Rate \| Maximum \| Obligations of U.S. Government entities and agencies
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	3	3
Recurring \| Discount Rate \| Maximum \| SBA servicing assets and Interest only strip
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	12.25	10.89
Recurring \| Prepayment speed \| Minimum \| SBA servicing assets and Interest only strip
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	14.43
Servicing asset measurement input		14.04
Recurring \| Prepayment speed \| Maximum \| SBA servicing assets and Interest only strip
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	17.12	17.71
Non-recurring fair value measurements \| Estimated selling costs \| Impaired Loans
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input	6	6
Non-recurring fair value measurements \| Estimated selling costs \| Foreclosed real estate
Fair value measurement inputs and valuation techniques
Available for sale securities measurement input		6

Value of input used to measure investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Indicates type of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleTypeExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of input used to measure servicing asset.

+ References

+ Details

Name:	us-gaap_ServicingAssetMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Indicates measurement input for servicing asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_ServicingAssetMeasurementInputExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=mcbs_SbaServicingAssetAndInterestOnlyStripMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=mcbs_ImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=mcbs_ForeclosedRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputPrepaymentRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputQuotedPriceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: