INVESTMENTS - Activity in Investments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Investments rollforward
Opening balance	$ 1,806
Additions/transfers during the period		$ 0
Net gain (loss) on securities sold	(100)
Unrealized gain (loss) on securities held	618
Fair Value end of the period	2,424
Marketable equity securities
Investments rollforward
Opening balance	1,644
Unrealized gain (loss) on securities held	618
Fair Value end of the period	2,262
Warrants
Investments rollforward
Opening balance	162
Fair Value end of the period	$ 162

Gross realized gains (losses) on equity securities.

No definition available.

Name:	mux_AvailableForSaleAndTradingSecuritiesGrossUnrealizedGainLoss
Namespace Prefix:	mux_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	mux_InvestmentsRollforward
Namespace Prefix:	mux_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Cash flow for purchase of available for sale and trading securities.

+ References

No definition available.

+ Details

Name:	mux_PaymentsToAcquireAvailableForSaleAndTradingSecurities
Namespace Prefix:	mux_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740

+ Details

Name:	us-gaap_EquitySecuritiesFvNi
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123583765&loc=SL75117546-209714

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

+ Details

Name:	us-gaap_EquitySecuritiesFvNiRealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=mux_WarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: