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ASSET RETIREMENT OBLIGATIONS (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2019 | Dec. 31, 2018
Reclamation obligations |  |
Reclamation Adjustment | $ 1.1 |
Black Fox |  |
Reclamation obligations |  |
Reclamation Adjustment | 5.3 |
Gold Bar mine |  |
Reclamation obligations |  |
Reclamation Adjustment | $ 4.2 | $ 3.6

X
- Definition Amount of reclamation adjustments during the period. + References No definition available. + Details
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Namespace Prefix: | mux_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | mux_MineralPropertyNameAxis=mux_BlackFoxMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mux_MineralPropertyNameAxis=mux_GoldBarMineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |