INCOME AND MINING TAXES - Changes to Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation allowance
Balance at Beginning of Period	$ 111,621	$ 122,768	$ 129,794
Additions	51,220	1,430	6,873
Deductions	(39,193)	(12,577)	(13,899)
Balance at End of Period	123,648	$ 111,621	$ 122,768
Black Fox
Valuation allowance
Change in valuation allowance	$ 12,000