INCOME AND MINING TAXES - Deferred Income Tax Recovery (Expense) and Net Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax recovery (expense)
United States	$ 2,420	$ 2,185	$ 10,349
Foreign	1,424	585	5,020
Deferred tax benefit	3,844	2,770	15,369
Net income (loss) before tax:
United States	(22,319)	(27,001)	(19,913)
Foreign	(41,272)	(20,639)	(6,090)
Loss before income and mining taxes	$ (63,591)	$ (47,640)	$ (26,003)