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ASSET RETIREMENT OBLIGATION: (Details)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Jun. 24, 2019
Mar. 31, 2022
USD ($)
Sep. 30, 2022
USD ($)
item
Sep. 30, 2021
USD ($)
Dec. 31, 2019
USD ($)
Jan. 31, 2022
USD ($)
ASSET RETIREMENT OBLIGATION:            
Maximum annual guarantees secured 50.00%          
Percentage of guarantee for Lima complex     50.00%      
Percentage of security for LOC     50.00%      
Total guarantees           $ 66.3
Asset retirement obligation activity            
Balance at the beginning of the year   $ 562.9 $ 562.9 $ 545.0    
Changes in estimates     43.3   $ 28.1  
Closure payments     (4.9) (3.7)    
Accretion expense     19.5 18.3    
Balance at the end of the year     $ 620.8 $ 559.6    
Peru            
ASSET RETIREMENT OBLIGATION:            
Period after which successive reviews are required by the law (in years)     5 years      
Number of units with future closure costs recognized as an asset retirement obligation | item     3      
Mexico            
Asset retirement obligation activity            
Changes in estimates   $ 43.3