DESCRIPTION OF THE BUSINESS: (Details) $ in Millions			3 Months Ended
	Apr. 16, 2020 USD ($)	Apr. 15, 2020 USD ($)	Mar. 31, 2020 employee $ / lb $ / item
Percentage of ownership interest held by the parent company			88.90%
Percentage of operating over production capacity during COVID-19 time			90.00%
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
Number of employees working on site under strict safety measures			3,499
Percentage workforce working on site under strict safety measures			39.00%
Number of employees working from home			5,468
Mexico
Number of employees working on site under strict safety measures			6,333
Percentage workforce working on site under strict safety measures			40.00%
Number of employees working from home			8,751
Subsequent Events | Fixed-rate senior unsecured notes issued April 2010
Repayment of debt | $	$ 410.8	$ 400.0