CASH AND CASH EQUIVALENTS AND RESTRICTED CASH (Details) $ in Thousands, $ in Millions				3 Months Ended		12 Months Ended
	Mar. 29, 2019 USD ($)	Dec. 20, 2018 USD ($)	Dec. 19, 2017 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 CAD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2017 USD ($)
Cash and cash equivalents (note 16)				$ 11,907			$ 15,756
Restricted cash				14,762			14,685
Restricted cash included in other long-term assets				48			48
Total cash, cash equivalents, and restricted cash				26,717	$ 38,741		30,489		$ 37,153
Net proceeds	$ 20,300
Generative exploration activities				14,800
Flow Through Common Shares
Net proceeds		$ 14,900	$ 10,000			$ 20.0	$ 14,900	$ 12.9	$ 10,000
Restricted cash spent for Timmins exploration activities				$ 400	$ 1,200