DESCRIPTION OF THE BUSINESS: (Details) $ in Millions		9 Months Ended
	Apr. 15, 2020 USD ($)	Sep. 30, 2020 USD ($) $ / lb $ / item
Percentage of ownership interest held by the parent company		88.90%
Percentage of operating over production capacity during COVID-19 time		96.00%
Pandemic related expenses		$ 18.9
Copper price assumption | $ / lb		2.00
Molybdenum price assumption | $ / item		4.00
Minimum
Projected discounted cash flows in excess of the carrying amounts of long lived assets by margins		1.2
Maximum
Projected discounted cash flows in excess of the carrying amounts of long lived assets by margins		4.8
Peru
Percentage workforce working on site under strict safety measures		67.00%
Percentage of workforce not working		33.00%
Mexico
Percentage workforce working on site under strict safety measures		97.00%
Percentage of workforce not working		3.00%
Fixed-rate senior unsecured notes issued April 2010
Repayment of debt	$ 400.0