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INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE (Details) (USD $) | 12 Months Ended | 11 Months Ended | 3 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2012 | Dec. 31, 2013 | Jan. 24, 2012
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |
Ownership interest (as a percent) | 100.00%us-gaap_EquityMethodInvestmentOwnershipPercentage |  |  |  |  |
Income (loss) on investment in Minera Santa Cruz S.A. (net of amortization) | $ (5,284,000)us-gaap_IncomeLossFromEquityMethodInvestments | $ 846,000 us-gaap_IncomeLossFromEquityMethodInvestments | $ 20,835,000 us-gaap_IncomeLossFromEquityMethodInvestments |  |  |
Impairment of investment in MSC | (21,162,000)us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment | (95,878,000)us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment |  |  |  |
Deferred tax liability related to mineral properties transferred | (214,000)us-gaap_DeferredTaxLiabilitiesInvestments |  |  |  |  |
(Gain) loss on sale of assets | (26,000)us-gaap_GainLossOnSaleOfPropertyPlantEquipment | 6,743,000 us-gaap_GainLossOnSaleOfPropertyPlantEquipment | (1,110,000)us-gaap_GainLossOnSaleOfPropertyPlantEquipment |  |  |
Dividends received | 9,483,000 us-gaap_ProceedsFromDividendsReceived | 1,826,000 us-gaap_ProceedsFromDividendsReceived | 9,770,000 us-gaap_ProceedsFromDividendsReceived |  |  |
MSC |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |
Ownership interest (as a percent) | 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 49.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember
Income (loss) on investment in Minera Santa Cruz S.A. (net of amortization) | (5,284,000)us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 846,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember |  | 20,835,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember |  |
Equity method investment, overstatement of income from prior year recorded in current period | 21,200,000 mux_EquityMethodInvestmentOverstatementOfNetIncomeAfterTax / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 95,900,000 mux_EquityMethodInvestmentOverstatementOfNetIncomeAfterTax / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember |  |  |  |
Impairment of investment in MSC | (21,162,000)us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | (95,878,000)us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember |  |  |  |
Carrying value of properties, net of tax |  | 35,857,000 mux_MineralPropertyInterestsTransferNetOfTax / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember |  |  |  |
Dividends received | 9,500,000 us-gaap_ProceedsFromDividendsReceived / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember | 1,800,000 us-gaap_ProceedsFromDividendsReceived / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember |  |  |  |
MSC | Exploration properties in Santa Cruz, Argentina | Vend-in agreement |  |  |  |  |  |
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE |  |  |  |  |  |
Deferred tax liability related to mineral properties transferred |  | 17,300,000 us-gaap_DeferredTaxLiabilitiesInvestments / mux_MineralPropertyNameAxis = mux_ExplorationPropertiesLocatedInSantaCruzProvinceArgentinaMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember / us-gaap_TypeOfArrangementAxis = mux_VendInAgreementMember |  |  | 17,300,000 us-gaap_DeferredTaxLiabilitiesInvestments / mux_MineralPropertyNameAxis = mux_ExplorationPropertiesLocatedInSantaCruzProvinceArgentinaMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember / us-gaap_TypeOfArrangementAxis = mux_VendInAgreementMember |
(Gain) loss on sale of assets |  |  |  |  | $ 0 us-gaap_GainLossOnSaleOfPropertyPlantEquipment / mux_MineralPropertyNameAxis = mux_ExplorationPropertiesLocatedInSantaCruzProvinceArgentinaMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = mux_MineraSantaCruzSAMember / us-gaap_TypeOfArrangementAxis = mux_VendInAgreementMember |

X
- Definition Represents the overstatement of after-tax net income, relating to the prior year, reported by an equity method investment of the entity which was deemed an immaterial error. + References No definition available. + Details
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