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INCOME TAXES: (Details) (USD $)
 3 Months Ended 9 Months Ended 1 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Peruvian operations
Sep. 30, 2013
Peruvian operations
Sep. 30, 2014
Peruvian operations
Minimum
Sep. 30, 2014
Peruvian operations
Maximum
Jan. 31, 2014
Mexican Operations
Sep. 30, 2014
Mexican Operations
INCOME TAXES:                    
Income tax provision $ 173,949,000 $ 197,885,000 $ 603,880,000 $ 604,634,000            
Effective income tax rate (as a percent)     38.30% 33.50%            
Increase in effective tax rate (as a percent)     4.00%              
Effect on tax rate (as a percent)     0.80%              
Components of the income tax provision                    
Statutory income tax provision     504,100,000 568,300,000            
Royalty         6,600,000 7,700,000        
Special mining tax         28,300,000 28,600,000        
Total income tax provision 173,949,000 197,885,000 603,880,000 604,634,000            
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         25,500,000 26,900,000        
Provision for royalty tax         6,600,000 7,700,000        
Provision for royalty tax                   64,900,000
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         28,300,000 28,600,000        
Changes in the entity's uncertain tax positions $ 0   $ 0