SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stockpiles, Proven and Probable Reserves (Details)	12 Months Ended
Dec. 31, 2018
Stockpiles, Ore on Leach Pads, In-process Inventory, Precious Metals Inventory and Materials and Supplies:
Period for determining current portion of stockpiles, ore on leach pad, in-process inventory and materials and supplies	12 months
Period within which Stockpiles, ore on leach pads, in-process inventory and materials and supplies are not expected to be processed, classified as long-term	12 months

Represents the period within which ore stockpile inventories are not expected to be processed and classified as long-term.

No definition available.

Name:	mux_PeriodForClassifyingOreStockpileInventoryAsLongTerm
Namespace Prefix:	mux_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration