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STOCK BASED COMPENSATION (Details) (USD $)
 0 Months Ended 12 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended
Oct. 19, 2006
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Jan. 19, 2012
Oct. 03, 2005
Oct. 02, 2005
Dec. 31, 2012
Minera Andes
Jan. 24, 2012
Minera Andes
Replacement options
Dec. 31, 2012
Certain employees, directors and consultants
item
Dec. 31, 2011
Certain employees, directors and consultants
Dec. 31, 2010
Certain employees, directors and consultants
STOCK-BASED COMPENSATION                        
Number of shares of common stock reserved for issuance 9,000,000       13,500,000 5,000,000 3,500,000          
Number of shares increased under the US Gold Plan 4,000,000                      
Maximum number of shares that may be subject to grants of options to an individual in a calendar year 1,000,000                      
Number of employees to whom stock options were granted                   1    
Stock options granted (in shares)   300,000 947,000 726,000           300,000 900,000 700,000
Exercise price of options granted (in dollars per share)   $ 5.80 $ 7.10 $ 2.51           $ 5.80 $ 7.10 $ 2.51
Vesting period of options                   3 years    
Exercise period of options                   10 years    
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)     1.74% 2.18%         0.02%      
Risk-free interest rate, high end of range (as a percent)     2.33% 2.97%         0.39%      
Volatility factor of the expected market price of common stock (as a percent)   76.00%                    
Volatility factor of the expected market price of common stock, low end of range (as a percent)     90.00% 87.00%         46.00%      
Volatility factor of the expected market price of common stock, high end of range (as a percent)     100.00% 94.00%         77.00%      
Weighted-average expected life of option   6 years 6 years 7 months 6 days 6 years 4 months 24 days         1 year 4 months 24 days      
Weighted-average grant date fair value (in dollars per share)   $ 3.80 $ 4.86 $ 2.84                
Stock option expense   $ 3,400,000 $ 2,700,000 $ 1,600,000       $ 1,300,000        
Shares                        
Balance at the beginning of the period (in shares)   3,870,000 3,086,000 2,632,000                
Granted (in shares)   300,000 947,000 726,000           300,000 900,000 700,000
Shares of common stock issued upon exercise of stock options   (445,000) (163,000) (109,000)                
Forfeited (in shares)   (128,000)   (100,000)                
Expired (in shares)   (36,000)   (63,000)       (48,000)        
Balance at the end of the period (in shares)   3,561,000 3,870,000 3,086,000                
Exercisable at the end of the period (in shares)   2,503,000           625,650        
Weighted Average Exercise Price                        
Balance at the beginning of the period (in dollars per share)   $ 3.24 $ 2.02 $ 2.13                
Granted (in dollars per share)   $ 5.80 $ 7.10 $ 2.51           $ 5.80 $ 7.10 $ 2.51
Exercised (in dollars per share)   $ 1.84 $ 2.52 $ 1.86                
Forfeited (in dollars per share)   $ 6.27   $ 8.30                
Expired (in dollars per share)   $ 7.96   $ 2.71                
Balance at the end of the period (in dollars per share)   $ 3.47 $ 3.24 $ 2.02                
Exercisable (in dollars per share)   $ 2.47                    
Weighted Average Remaining Contractual Life                        
Outstanding at the end of the period   6 years 7 months 6 days 7 years 7 months 6 days 8 years 1 month 6 days                
Exercisable at the end of the period   6 years                    
Intrinsic Value                        
Outstanding at the end of the period (in dollars)   4,887,000 864,000 225,000                
Exercisable at the end of the period (in dollars)   4,619,000                    
Additional disclosures                        
Unrecognized compensation expense on non-vested stock options (in dollars)   $ 1,100,000                    
Non-vested stock options outstanding (in shares)   1,100,000                    
Weighted-average period of recognition   1 year 2 months 12 days