XML 49 R36.htm IDEA: XBRL DOCUMENT v3.8.0.1
INCOME TAXES: (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Income Taxes        
Statutory income tax provision $ 212.3 $ 148.5    
Peruvian royalty 1.7 0.4    
Mexican royalty 16.1 21.4    
Peruvian special mining tax 6.5 5.9    
Income tax provision $ 236.6 $ 176.2    
Effective income tax rate (as a percent) 33.60% 36.30%    
U.S. statutory rate (as a percent)       35.00%
Non-cash tax expense for estimated tax effect       $ 785.9
Changes in the entity's uncertain tax positions $ 0.0      
Peru        
Income Taxes        
Peruvian royalty $ 1.7 $ 0.4    
Increment in operating income margin for royalty tax (as a percent) 5.00%      
Increase in royalty tax rate for each 5% increase up to 12% increase in operating income margin (as a percent) 0.75%      
Royalty charges $ 7.1 5.5    
Increase in special mining tax rate for each 5% increase up to 85% increase in operating income margin (as a percent) 0.40%      
Increment in operating income margin (as a percent) 5.00%      
Accrued special mining tax $ 6.5 5.9    
Peru | Minimum        
Income Taxes        
Mining royalty tax (as a percent) 1.00%      
Royalty charge assessed as a percentage of net sales 1.00%      
Special mine tax (as a percent) 2.00%      
Increment in operating income margin (as a percent) 2.00%      
Peru | Maximum        
Income Taxes        
Mining royalty tax (as a percent) 12.00%      
Operating income margin for royalty tax (as a percent) 10.00%      
Increment in operating income margin for royalty tax (as a percent) 12.00%      
Special mine tax (as a percent) 8.40%      
Operating income margin (as a percent) 10.00%      
Increment in operating income margin (as a percent) 85.00%      
Mexico        
Income Taxes        
Mexican royalty $ 16.1 $ 21.4    
Mining royalty tax (as a percent) 7.50%      
Additional royalty tax over net sales from sales of gold, silver and platinum (as a percent) 0.50%      
Royalty expense paid $ 87.7      
Forecast        
Income Taxes        
U.S. statutory rate (as a percent)     21.00%  
Beginning in 2018        
Income Taxes        
BEAT tax rate (as a percent) 5.00%      
2019 - 2025        
Income Taxes        
BEAT tax rate (as a percent) 10.00%      
After 2025        
Income Taxes        
BEAT tax rate (as a percent) 12.50%