INCOME AND MINING TAXES - Tax Effects of Temporary Differences (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforward	$ 55,515	$ 72,078
Mineral properties	62,345	59,905
Other temporary differences	15,198	862
Total gross deferred tax assets	133,058	132,845
Less: valuation allowance	(124,153)	(123,648)	$ (111,621)	$ (122,768)
Valuation allowances	500
Net deferred tax assets	8,905	9,197
Deferred tax liabilities:
Acquisition mineral property interests	(15,331)	(17,627)
Total deferred tax liabilities	(15,331)	(17,627)
Total net deferred tax liability	$ (6,426)	(8,430)
Gold Bar project
Deferred tax assets:
Net deferred tax assets		$ 6,400