COMMITMENTS AND CONTINGENCIES: - Environmental matters (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2011 person category
Environmental costs
Environmental capital investment	$ 60.6	$ 24.6
Peru
Environmental costs
Environmental capital investment	2.9	4.0
Mexico
Environmental costs
Environmental capital investment	$ 57.7	$ 28.6
Number of categories of collective actions | category			3
Minimum number of people claiming injury due to collective action initiative in Civil Federal Procedures Code (CFPC) | person			30