COMMITMENTS AND CONTINGENCIES - Streaming Agreement (Details) $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 25, 2017 $ / oz	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Other commitments
Revenues		$ 26,896	$ 13,430	$ 102,360	$ 43,373
Black Fox
Other commitments
Obligation to sell (as a percent)	8.00%
Revenues		$ 500	$ 0	$ 1,800	$ 0
Pike River property
Other commitments
Obligation to sell (as a percent)	6.30%
Long Term Gold Price (in dollars per ounce) | $ / oz	539
Pike River property | Maximum
Other commitments
Inflation adjustment (as a percent)	2.00%