LONG-TERM DEBT - Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Long-term debt
Balance, beginning of year	$ 48,160	$ 49,516
Interest expense	5,581	5,394
Interest payments	(4,875)	(4,875)
Bonus Interest - Equity based financing fee		(1,875)
Balance, end of year	$ 48,866	$ 48,160

Represents information pertaining to debt amendment equity.

No definition available.

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

- Definition

Reflects the total carrying amount as of the balance sheet date of debt and related party debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

No definition available.

+ Details

Name:	mux_DebtAndDebtToRelatedPartyNoncurrent
Namespace Prefix:	mux_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the required periodic payments applied to interest.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPaymentInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate amount of interest paid or due on all long-term debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.8)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph (a)

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph (b)
-Subparagraph (1)

+ Details

Name:	us-gaap_InterestExpenseLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtNoncurrentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration