OPERATING SEGMENT REPORTING (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Operating Segment Reporting
Revenues	$ 26,896	$ 13,430	$ 102,360	$ 43,373
Revision of estimates and accretion of reclamation obligations	(314)	(320)	(896)	(541)
Property holding costs	(1,975)	(1,979)	(3,575)	(3,590)
General and administrative expenses	(4,576)	(4,734)	(15,577)	(13,105)
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(4,973)	(462)	(7,450)	(535)
Depreciation			(6,839)	(1,125)
Interest and other expense	(832)	(303)	(612)	(478)
Revision of estimates and accretion of reclamation obligations	(314)	(320)	(896)	(541)
Gain on sale of assets			(99)	11
Gain (loss) on sale of marketable equity securities (note 2)			(767)	840
Other-than-temporary impairment on marketable equity securities		(356)		(356)
Other-than-temporary impairment on marketable equity securities (note 2)		356		356
Unrealized (loss) gain on derivative instrument	134	(933)	(731)	136
(Gain) on disposal of fixed assets			(99)	11
Foreign currency gain	1,159	(276)	3,568	799
Net loss before income and mining taxes	(14,903)	(8,636)	(28,772)	(15,867)	$ 18,700
Long-Lived Assets	542,876		542,876		505,265
Investment in MSC	133,254		133,254		150,064
Mexico
Operating Segment Reporting
Cost of goods and services sold				(24,193)
Property holding costs	(1,001)	(1,044)	(2,191)	(2,089)
General and administrative expenses	(709)	(715)	(2,338)	(2,594)
Segment income (loss)	3,538	1,600	15,698	9,691
MSC
Operating Segment Reporting
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(4,973)	(462)	(7,450)	(535)
Segment income (loss)	(4,973)	(462)	(7,450)	(535)
Los Azules
Operating Segment Reporting
Property holding costs	(27)		(67)	(48)
General and administrative expenses	(84)	(320)	(832)	(949)
Segment income (loss)	(540)	(685)	(6,406)	(8,504)
U.S.
Operating Segment Reporting
Property holding costs	(908)	(935)	(1,183)	(1,453)
General and administrative expenses	(1,630)	(441)	(3,988)	(1,226)
Segment income (loss)	(3,577)	(3,041)	(9,361)	(6,778)
Canada
Operating Segment Reporting
Property holding costs	(39)		(134)
General and administrative expenses	39	(32)	(101)	(58)
Segment income (loss)	(6,869)	(169)	(10,691)	(325)
Total Segment
Operating Segment Reporting
Cost of goods and services sold				(24,193)
Property holding costs	(1,975)	(1,979)	(3,575)	(3,590)
General and administrative expenses	(2,384)	(1,508)	(7,259)	(4,827)
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(4,973)	(462)	(7,450)	(535)
Segment income (loss)	(12,421)	(2,757)	(18,210)	(6,451)
Corporate & Other
Operating Segment Reporting
Revision of estimates and accretion of reclamation obligations	(314)	(320)	(896)	(541)
Other exploration costs		(149)		(424)
General and administrative expenses	(2,192)	(3,226)	(8,318)	(8,278)
Depreciation	(279)	(316)	(912)	(1,125)
Interest and other expense	(832)	(303)	(612)
Revision of estimates and accretion of reclamation obligations	(314)	(320)	(896)	(541)
Interest income and other income				(478)
Gain on sale of assets			99	11
Gain (loss) on sale of marketable equity securities (note 2)			(767)	840
Unrealized fair value loss on marketable equity securities			1,795
Other-than-temporary impairment on marketable equity securities	(158)	(356)		(356)
Unrealized (loss) gain on derivative instrument	134	(933)	(731)	136
Foreign currency gain	1,159	(276)	3,568	799
MSC
Operating Segment Reporting
Revenues	47,814	52,722	150,748	161,900
Cost of goods and services sold	(48,193)	(43,596)	(135,007)	(132,710)
(Loss) from investment in Minera Santa Cruz S.A. (net of amortization)	(4,973)	(462)	(7,450)	(535)
Net loss before income and mining taxes	(9,649)	1,422	(9,395)	7,727
Investment in MSC	133,254		133,254		150,064	$ 162,320
Canada
Operating Segment Reporting
Revenues	11,395		47,061
Long-Lived Assets	85,903		85,903		85,179
Mexico
Operating Segment Reporting
Revenues	15,501	13,430	55,299	43,373
Long-Lived Assets	28,361		28,361		35,446
United States
Operating Segment Reporting
Long-Lived Assets	103,868		103,868		43,086
United States | Gold Bar Complex
Operating Segment Reporting
Mine Construction Costs	28,500		54,900
Construction-in-progress					61,500
Argentina
Operating Segment Reporting
Long-Lived Assets	324,744		324,744		341,554
Argentina | MSC
Operating Segment Reporting
Investment in MSC	133,300		133,300		$ 151,000
Gold and silver sales
Operating Segment Reporting
Revenues	26,896	13,430	101,743	43,373
Gold and silver sales | Mexico
Operating Segment Reporting
Revenues	15,501	13,430	55,299	43,373
Gold and silver sales | Canada
Operating Segment Reporting
Revenues	11,395		46,444
Gold and silver sales | Total Segment
Operating Segment Reporting
Revenues	26,896	13,430	101,743	43,373
Other revenue
Operating Segment Reporting
Revenues			617
Other revenue | Canada
Operating Segment Reporting
Revenues			617
Other revenue | Total Segment
Operating Segment Reporting
Revenues			617
Production costs applicable to sales
Operating Segment Reporting
Cost of goods and services sold	(20,320)	(8,649)	(70,970)	(24,193)
Production costs applicable to sales | Mexico
Operating Segment Reporting
Cost of goods and services sold	(8,452)	(8,649)	(30,881)
Production costs applicable to sales | Canada
Operating Segment Reporting
Cost of goods and services sold	(11,868)		(40,089)
Production costs applicable to sales | Total Segment
Operating Segment Reporting
Cost of goods and services sold	(20,320)	(8,649)	(70,970)
Mine development
Operating Segment Reporting
Cost of goods and services sold	(1,505)	(1,382)	(2,595)	(3,217)
Mine development | Mexico
Operating Segment Reporting
Cost of goods and services sold	(1,505)	(273)	(2,595)	(605)
Mine development | U.S.
Operating Segment Reporting
Cost of goods and services sold		(1,109)		(2,612)
Mine development | Total Segment
Operating Segment Reporting
Cost of goods and services sold	(1,505)	(1,382)	(2,595)	(3,217)
Exploration
Operating Segment Reporting
Cost of goods and services sold	(8,160)	(2,356)	(28,721)	(13,886)
Exploration | Mexico
Operating Segment Reporting
Cost of goods and services sold	(296)	(1,149)	(1,596)	(4,201)
Exploration | Los Azules
Operating Segment Reporting
Cost of goods and services sold	(429)	(365)	(5,507)	(7,507)
Exploration | U.S.
Operating Segment Reporting
Cost of goods and services sold	(1,039)	(556)	(4,190)	(1,487)
Exploration | Canada
Operating Segment Reporting
Cost of goods and services sold	(6,396)	(137)	(17,428)	(267)
Exploration | Total Segment
Operating Segment Reporting
Cost of goods and services sold	$ (8,160)	$ (2,207)	$ (28,721)	$ (13,462)