Decommissioning And Restoration Liability - Additional Information (Detail) - CAD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Decommissioning And Restoration Liability [Abstract]
Increase decrease in discounted cash flows of decommissioning restoration and rehabilitation provision	$ 13,364	$ 2,490

The increase (decrease) in estimated discounted cash flows of decommissioning restoration and rehabilitation provision.

No definition available.

Name:	mpvd_IncreaseDecreaseInDiscountedCashFlowsOfDecommissioningRestorationAndRehabilitationProvision
Namespace Prefix:	mpvd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration