REVENUE: - Provisionally prices sales (Details) lb in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) lb $ / item
Copper
Provisionally priced sales:
Provisional price sales adjustment amounts included in accounts receivable and net sales | $	$ 3.7
Copper | July 2019 to November 2019
Provisionally priced sales:
Sales volume (in million lbs.) | lb	141.2
Provisional price | $ / item	3.03
Molybdenum
Provisionally priced sales:
Provisional price sales adjustment amounts included in accounts receivable and net sales | $	$ 2.8
Molybdenum | July 2019 to September 2019
Provisionally priced sales:
Sales volume (in million lbs.) | lb	12.8
Provisional price | $ / item	8.15