VARIABLE INTEREST ENTITIES (Details) - Variable Interest Entity, Primary Beneficiary [Member]	Jun. 30, 2021 USD ($) Entity
Nonconsolidated Variable Interest Entities [Abstract]
Number of unconsolidated VIEs \| Entity	13
Total Nonconsolidated VIEs [Abstract]
Fair value of investments in VIEs	$ 38,006,233
Carrying value of variable interests - assets	38,529,875
Carrying value of variable interests - liabilities	0
Maximum Exposure to Loss [Abstract]
Limited Partnership Interest	$ 38,529,875

No definition available.

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- Definition

The number of unconsolidated variable interest entities in limited partnerships and limited liability companies.

+ References

No definition available.

+ Details

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- Definition

Fair value of the investment in variable interest entities at close of period.

+ References

No definition available.

+ Details

Name:	mrc_VariableInterestEntityFairValueInvestment
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), when the reporting entity is not the VIE's primary beneficiary.

+ References

No definition available.

+ Details

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- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), when the reporting entity is not the VIE's primary beneficiary.

+ References

No definition available.

+ Details

Name:	mrc_VariableInterestEntityNonconsolidatedLiabilitiesCarryingAmount
Namespace Prefix:	mrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	mrc_VariableInterestEntityPrimaryBeneficiaryDisclosuresAbstract
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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123419778&loc=d3e5747-111685

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=123419778&loc=d3e5728-111685

+ Details

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Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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- Details

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