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STOCK-BASED COMPENSATION (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
STOCK BASED COMPENSATION      
Stock option expense $ 0.4us-gaap_AllocatedShareBasedCompensationExpense $ 0.4us-gaap_AllocatedShareBasedCompensationExpense  
Principal assumptions used in applying the Black-Scholes option pricing model for the awards      
Risk-free interest rate (as a percent) 1.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate    
Volatility factor of the expected market price of common stock (as a percent) 75.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate    
Weighted-average expected life of option 3 years 6 months    
Weighted-average grant date fair value (in dollars per share) $ 0.56us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue    
Certain employees and directors      
STOCK BASED COMPENSATION      
Stock options granted (in shares) 0.1us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= mux_EmployeesAndDirectorsMember
  0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= mux_EmployeesAndDirectorsMember
Exercise price of options granted (in dollars per share) $ 1.06us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= mux_EmployeesAndDirectorsMember
   
Vesting period of options 3 years    
Exercisable period of options 5 years