REVENUE: - Provisionally prices sales (Details) lb in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) lb $ / item
Copper
Provisionally priced sales:
Provisional price sales adjustment amounts included in accounts receivable and net sales | $	$ 15.3
Copper | July 2019 to November 2019
Provisionally priced sales:
Sales volume (in million lbs.) | lb	83.5
Provisional price | $ / item	2.24
Molybdenum
Provisionally priced sales:
Provisional price sales adjustment amounts included in accounts receivable and net sales | $	$ 20.6
Molybdenum | July 2019 to September 2019
Provisionally priced sales:
Sales volume (in million lbs.) | lb	14.8
Provisional price | $ / item	8.43