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STOCK-BASED COMPENSATION (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Jan. 19, 2012
STOCK-BASED COMPENSATION          
Number of shares of common stock reserved for issuance before amendment         9
Number of shares of common stock reserved for issuance         13.5
Stock option expense $ 0.5 $ 0.7 $ 2.1 $ 1.2  
Principal assumptions used in applying the Black-Scholes option pricing model for the awards          
Risk-free interest rate (as a percent)     0.97%    
Risk-free interest rate, low end of range (as a percent)       2.33%  
Risk-free interest rate, high end of range (as a percent)       3.09%  
Volatility factor of the expected market price of common stock (as a percent)     75.00%    
Volatility factor of the expected market price of common stock, low end of range (as a percent)       90.00%  
Volatility factor of the expected market price of common stock, high end of range (as a percent)       99.00%  
Weighted-average expected life of option     6 years 6 years 7 months 6 days  
Weighted-average grant date fair value (in dollars per share)     $ 3.80 $ 5.31  
Minera Andes
          
STOCK-BASED COMPENSATION          
Stock option expense $ 0.3   $ 1.0    
Chief Operating Officer
          
STOCK-BASED COMPENSATION          
Stock options granted (in shares)     0.3    
Exercise price of options granted (in dollars per share)     $ 5.80    
Certain employees, directors and consultants
          
STOCK-BASED COMPENSATION          
Stock options granted (in shares)       0.9  
Exercise price of options granted (in dollars per share)       $ 7.10  
Vesting period of options     3 years    
Exercise period of options     10 years