COMMITMENTS AND CONTINGENCIES - Surety, Reclamation Bonds and Flow-Through Common Shares (Details) $ in Thousands, $ in Millions								1 Months Ended	12 Months Ended
	Dec. 20, 2018 CAD ($)	Dec. 20, 2018 USD ($)	Dec. 20, 2017 USD ($)	Sep. 22, 2017 USD ($)	Aug. 25, 2017 USD ($)	Jul. 01, 2017 USD ($)	Jun. 23, 2017 USD ($)	Jul. 31, 2017 USD ($)	Dec. 31, 2018 CAD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Reclamation Bonds
Other assets										$ 5,872	$ 10,718
Amount raised or spent in connection with the equity issuance				$ 43,200						918	39,397
Surety Bonds
Reclamation Bonds
Face amount							$ 20,000
Percentage of annual fees on surety bonds							2.00%
Surety bonds upfront deposit amount					$ 15,000		$ 0	$ 500
Surety Bonds | Tonkin Project
Reclamation Bonds
Surety bond draw down						$ 3,600
Surety Bonds | Nevada Exploration Properties
Reclamation Bonds
Surety bond draw down						$ 1,300
Surety Bonds | Gold Bar project
Reclamation Bonds
Surety bond draw down					$ 15,000
Reclamation Bonds
Reclamation Bonds
Reclamation bonding obligation										19,900
Black Fox
Reclamation Bonds
Surety bonding obligation									$ 20.6	15,900
Outstanding surety bonds										20,000
Timmins
Reclamation Bonds
Surety bonds upfront deposit amount										100
Other assets
Reclamation Bonds
Other assets										100
Flow Through Common Shares
Reclamation Bonds
Amount raised or spent in connection with the equity issuance	$ 20.0	$ 14,900	$ 14,900							$ 11,145	$ 7,799