REVENUE: - Provisionally prices sales (Details) lb in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) lb $ / item
Copper
Provisionally priced sales:
Provisional price sales adjustment amounts included in accounts receivable and net sales | $	$ 15.4
Copper | July 2019 to November 2019
Provisionally priced sales:
Sales volume (in million lbs.) | lb	113.2
Provisional price | $ / item	2.73
Molybdenum
Provisionally priced sales:
Provisional price sales adjustment amounts included in accounts receivable and net sales | $	$ 28.8
Molybdenum | July 2019 to September 2019
Provisionally priced sales:
Sales volume (in million lbs.) | lb	18.0
Provisional price | $ / item	7.38