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INCOME TAXES: (Details) (USD $)
 3 Months Ended 6 Months Ended 1 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Peruvian operations
Jun. 30, 2013
Peruvian operations
Jun. 30, 2014
Peruvian operations
Minimum
Jun. 30, 2014
Peruvian operations
Maximum
Jan. 31, 2014
Mexican Operations
Jun. 30, 2014
Mexican Operations
INCOME TAXES:                    
Income tax provision $ 225,769,000 $ 167,870,000 $ 429,931,000 $ 406,749,000            
Effective income tax rate (as a percent)     39.80% 32.20%            
Increase in effective tax rate (as a percent)     4.70%              
Components of the income tax provision                    
Statutory income tax provision     361,600,000 380,700,000            
Royalty         2,100,000 5,000,000        
Special mining tax         19,600,000 21,100,000        
Total income tax provision 225,769,000 167,870,000 429,931,000 406,749,000            
Mining royalty tax (as a percent)             1.00% 12.00% 7.50%  
Royalty charge assessed as a percentage of net sales             1.00%      
Operating income margin for royalty tax (as a percent)               10.00%    
Increment in operating income margin for royalty tax (as a percent)             5.00% 12.00%    
Increase in royalty tax rate for each 5% increase up to 12% increase in operating income margin (as a percent)         0.75%          
Royalty charge         14,400,000 17,700,000        
Provision for royalty tax         2,100,000 5,000,000        
Provision for royalty tax                   46,600,000
Additional royalty tax over net sales from sales of gold, silver and platinum (as a percent)                 0.50%  
Special mine tax (as a percent)             2.00% 8.40%    
Operating income margin (as a percent)               10.00%    
Increment in operating income margin (as a percent)             5.00% 85.00%    
Increase in special mining tax rate for each 5% increase up to 85% increase in operating income margin (as a percent)         0.40%          
Accrued special mining tax         $ 19,600,000 $ 21,000,000