SUBSEQUENT EVENT (Details) - USD ($) $ in Thousands		6 Months Ended
	Jan. 29, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent events
Acquisition consideration paid		$ 72,417	$ 55
Subsequent Event | Alturas
Subsequent events
Acquisition consideration paid	$ 11,000
Future payment based on project decisions	20,000
Future payment to private individuals upon first production	10,000
Subsequent Event | Alturas | Maximum
Subsequent events
Acquisition consideration	$ 41,000
Subsequent Event | Alturas | Gold
Subsequent events
Net smelter return (NSR) (as a percent)	1.06%
Subsequent Event | Alturas | Copper
Subsequent events
Net smelter return (NSR) (as a percent)	1.59%