OPERATING SEGMENT REPORTING (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Operating Segment Reporting
Revenues	$ 15,640	$ 41,285	$ 41,285
Revision of estimates and accretion of reclamation obligations	(461)	(294)
Property holding costs	(1,608)	(1,411)
General and administrative expenses	(3,871)	(5,187)
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(2,310)	(212)
Interest and other expense	(513)	(134)
Revision of estimates and accretion of reclamation obligations	(461)	(294)
Foreign currency gain	163	927
Net (loss) income before tax	(10,018)	(6,349)
Long-Lived Assets	563,316		557,565
Investment in MSC	123,484		127,814
Mexico
Operating Segment Reporting
Property holding costs	(1,197)	(1,149)
General and administrative expenses	(1,202)	(829)
Segment income (loss)	(1,302)	8,480
MSC
Operating Segment Reporting
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(2,310)	(212)
Segment income (loss)	(2,310)	(212)
Los Azules
Operating Segment Reporting
Property holding costs	(20)	(40)
General and administrative expenses	(184)	(278)
Segment income (loss)	(1,117)	(3,525)
U.S.
Operating Segment Reporting
Property holding costs	(341)	(179)
General and administrative expenses	(195)	(863)
Segment income (loss)	(869)	(3,042)
Canada
Operating Segment Reporting
Property holding costs	(50)	(43)
General and administrative expenses	(28)	(88)
Segment income (loss)	(2,022)	(2,325)
Total Segment
Operating Segment Reporting
Property holding costs	(1,608)	(1,411)
General and administrative expenses	(1,609)	(2,058)
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(2,310)	(212)
Segment income (loss)	(7,620)	(624)
Corporate & Other
Operating Segment Reporting
Revision of estimates and accretion of reclamation obligations	(461)	(294)
General and administrative expenses	(2,262)	(3,129)
Depreciation	(152)	(360)
Interest and other expense	(513)	134
Revision of estimates and accretion of reclamation obligations	(461)	(294)
Gain (loss) on sale of marketable equity securities (note 2)	827	(2,735)
Foreign currency gain	163	927
MSC
Operating Segment Reporting
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(2,310)	(212)
Investment in MSC	123,484		127,814	$ 150,064
Canada
Operating Segment Reporting
Revenues	8,943		15,868
Long-Lived Assets	83,798		84,119
Mexico
Operating Segment Reporting
Revenues	5,798		25,417
Long-Lived Assets	25,873		26,524
United States
Operating Segment Reporting
Revenues	899
Long-Lived Assets	138,670		127,617
Argentina
Operating Segment Reporting
Long-Lived Assets	314,975		319,305
Argentina | MSC
Operating Segment Reporting
Investment in MSC	123,500		$ 127,800
Gold and silver sales
Operating Segment Reporting
Revenues	15,583	41,041
Gold and silver sales | Mexico
Operating Segment Reporting
Revenues	5,798	25,417
Gold and silver sales | U.S.
Operating Segment Reporting
Revenues	842
Gold and silver sales | Canada
Operating Segment Reporting
Revenues	8,943	15,624
Gold and silver sales | Total Segment
Operating Segment Reporting
Revenues	15,583	41,041
Other revenue
Operating Segment Reporting
Revenues	57	244
Other revenue | U.S.
Operating Segment Reporting
Revenues	57
Other revenue | Canada
Operating Segment Reporting
Revenues		244
Other revenue | Total Segment
Operating Segment Reporting
Revenues	57
Production costs applicable to sales
Operating Segment Reporting
Cost of goods and services sold	(13,168)	(26,394)
Production costs applicable to sales | Mexico
Operating Segment Reporting
Cost of goods and services sold	(3,925)	(13,608)
Production costs applicable to sales | U.S.
Operating Segment Reporting
Cost of goods and services sold	(748)
Production costs applicable to sales | Canada
Operating Segment Reporting
Cost of goods and services sold	(8,495)	(12,786)
Production costs applicable to sales | Total Segment
Operating Segment Reporting
Cost of goods and services sold	(13,168)	(26,394)
Mine development
Operating Segment Reporting
Cost of goods and services sold	(776)	(380)
Mine development | Mexico
Operating Segment Reporting
Cost of goods and services sold	(776)	(380)
Mine development | Total Segment
Operating Segment Reporting
Cost of goods and services sold	(776)	(380)
Exploration
Operating Segment Reporting
Cost of goods and services sold	(3,789)	(11,454)
Exploration | Mexico
Operating Segment Reporting
Cost of goods and services sold		(971)
Exploration | Los Azules
Operating Segment Reporting
Cost of goods and services sold	(913)	(3,207)
Exploration | U.S.
Operating Segment Reporting
Cost of goods and services sold	(484)	(2,000)
Exploration | Canada
Operating Segment Reporting
Cost of goods and services sold	(2,392)	(5,276)
Exploration | Total Segment
Operating Segment Reporting
Cost of goods and services sold	$ (3,789)	$ (11,454)