INCOME AND MINING TAXES - Deferred Income Tax Recovery (Expense) and Net Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax recovery (expense)
United States	$ 2,185	$ 10,349	$ 515
Foreign	585	5,020	3,234
Deferred tax recovery	2,770	15,369	3,749
Net income (loss) before tax:
United States	(27,001)	(19,913)	(13,959)
Foreign	(20,639)	(6,090)	31,265
(Loss) income before income and mining taxes	$ (47,640)	$ (26,003)	$ 17,306