INCOME AND MINING TAXES - Deferred Income Tax Recovery (Expense) and Net Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred income tax recovery (expense)
United States	$ 10,349	$ 515	$ (442)
Foreign	5,020	3,234	25,002
Deferred tax recovery	15,369	3,749	24,560
Net income (loss) before tax:
United States	(19,913)	(13,959)	(19,935)
Foreign	(6,090)	31,265	(25,075)
(Loss) Income before income and mining taxes	$ (26,003)	$ 17,306	$ (45,010)