SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	12 Months Ended
Dec. 31, 2019
NATURE OF OPERATIONS
Lease, Practical Expedients, Package	true
Lease, Practical Expedient, Use of Hindsight	true
Lease, Practical Expedient, Land Easement	true

Indicates (true false) whether practical expedient is elected to use land easements in determining lease term and in assessing impairment of right-of-use asset.

No definition available.

+ Details

Name:	mux_LeasePracticalExpedientLandEasement
Namespace Prefix:	mux_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether practical expedient is elected to use hindsight in determining lease term and in assessing impairment of right-of-use asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984

+ Details

Name:	us-gaap_LeasePracticalExpedientUseOfHindsight
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- Definition

Indicates (true false) whether practical expedients are elected for not reassessing whether any expired or existing contract is or contains lease, lease classification for expired or existing lease, and initial direct cost for any existing lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 10
-Section 65
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=119364159&loc=SL77916155-209984

+ Details

Name:	us-gaap_LeasePracticalExpedientsPackage
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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