SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Organization and Deferred Offering Costs (Details)	12 Months Ended
Jun. 30, 2021
Organization and Deferred Offering Costs [Abstract]
Amortization period of deferred offering costs	12 months

Amortization period of capitalized deferred offering costs in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

No definition available.

Name:	mrc_AmortizationPeriodOfDeferredOfferingCosts
Namespace Prefix:	mrc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration