INCOME AND MINING TAXES - Tax Effects of Temporary Differences (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforward	$ 72,078	$ 96,312
Mineral properties	59,905	14,195
Other temporary differences	862	1,114
Total gross deferred tax assets	132,845	111,621
Less: valuation allowance	(123,648)	(111,621)	$ (122,768)	$ (129,794)
Net deferred tax assets	9,197
Deferred tax liabilities:
Acquisition mineral property interests	(17,627)	(23,655)
Total deferred tax liabilities	(17,627)	(23,655)
Total net deferred tax liability	(8,430)	(23,655)
Minera Andes
Deferred tax liabilities:
Acquisition related deferred tax liability	6,200	$ 12,600
Gold Bar project
Deferred tax assets:
Net deferred tax assets	$ 6,400