INCOME AND MINING TAXES - Reconciliation of Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INCOME AND MINING TAXES.
(Loss) income before income and mining taxes	$ (26,003)	$ 17,306	$ (45,010)
Statutory tax rate (as a percent)	35.00%	34.00%	34.00%
US Federal and State tax recovery at statutory rate	$ (9,101)	$ 5,884	$ (15,303)
Reconciling items:
Equity pickup in MSC	(16)	(4,533)	(821)
Impairment of MSC			4,004
Deferred foreign income inclusion	21,002
Foreign tax credits	(16,628)
Tax rate changes	28,048
Revisions to prior year estimates	(573)	(828)	906
Adjustment for foreign tax rates	115	(501)	(1,230)
Other permanent differences	(1,761)	818	(15,694)
Unrealized foreign exchange rate (loss)/gain	2,469	5,972	9,389
NOL expires and revisions	(2,233)	586	1,215
Valuation allowance	(36,691)	(11,147)	(7,026)
Tax benefit	$ (15,369)	$ (3,749)	$ (24,560)