OPERATING SEGMENT REPORTING - Summary of Reportable Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Segment Reporting
Revenue from gold and silver sales	$ 37,129	$ 27,395	$ 101,575	$ 77,086
Depreciation and depletion	(6,025)	(4,570)	(16,677)	(16,080)
Gross profit (loss)	344	(701)	(583)	(13,261)
Advanced projects	(4,013)	(4,027)	(6,635)	(9,464)
Impairment of mineral property interests and plant and equipment (Note 8)				(83,805)
Loss from investment in Minera Santa Cruz S.A.	(2,650)	2,582	(5,077)	(1,139)
Other expenses				(1,968)
Segment loss	(12,564)	(6,569)	(30,412)	(121,398)
General and Administrative and other	(5,678)	(3,361)	(9,322)	(8,661)
Loss before income and mining taxes	(18,242)	(9,930)	(39,734)	(130,059)
Capital expenditures	11,128	594	21,452	9,140
United States Reportable Segment [Member]
Operating Segment Reporting
Depreciation and depletion	(2,140)	(2,099)	(6,208)	(8,527)
Gross profit (loss)	790	152	1,335	(9,261)
Advanced projects	(234)	(240)	(203)	(789)
Impairment of mineral property interests and plant and equipment (Note 8)				(83,805)
Other expenses				(1,390)
Segment loss	(876)	(2,483)	(2,755)	(100,480)
Capital expenditures	353	106	1,110	4,712
Canada
Operating Segment Reporting
Depreciation and depletion	(3,885)	(2,404)	(10,469)	(7,336)
Gross profit (loss)	707	(926)	1,875	(4,310)
Advanced projects	(871)	(2,784)	(2,058)	(5,609)
Other expenses				(578)
Segment loss	(4,981)	(4,899)	(12,715)	(14,931)
Capital expenditures	10,775	488	20,342	4,428
Mexico Reportable Segment [Member]
Operating Segment Reporting
Depreciation and depletion		(67)		(217)
Gross profit (loss)	(1,153)	73	(3,793)	310
Advanced projects	(1,872)	(1,003)	(3,338)	(3,066)
Segment loss	(3,021)	(1,357)	(7,145)	(3,219)
MSC
Operating Segment Reporting
Loss from investment in Minera Santa Cruz S.A.	(2,650)	2,582	(5,077)	(1,139)
Segment loss	(2,650)	2,582	(5,077)	(1,139)
Los Azules
Operating Segment Reporting
Advanced projects	(1,036)		(1,036)
Segment loss	(1,036)	(412)	(2,720)	(1,629)
Gold and silver sales
Operating Segment Reporting
Revenue from gold and silver sales	37,129	27,395	101,575	77,086
Gold and silver sales | United States Reportable Segment [Member]
Operating Segment Reporting
Revenue from gold and silver sales	21,683	13,042	60,919	38,129
Gold and silver sales | Canada
Operating Segment Reporting
Revenue from gold and silver sales	14,227	10,352	34,966	27,257
Gold and silver sales | Mexico Reportable Segment [Member]
Operating Segment Reporting
Revenue from gold and silver sales	1,219	4,001	5,690	11,700
Product [Member]
Operating Segment Reporting
Production costs applicable to sales	(30,760)	(23,526)	(85,481)	(74,267)
Product [Member] | United States Reportable Segment [Member]
Operating Segment Reporting
Production costs applicable to sales	(18,753)	(10,791)	(53,376)	(38,863)
Product [Member] | Canada
Operating Segment Reporting
Production costs applicable to sales	(9,635)	(8,874)	(22,622)	(24,231)
Product [Member] | Mexico Reportable Segment [Member]
Operating Segment Reporting
Production costs applicable to sales	(2,372)	(3,861)	(9,483)	(11,173)
Exploration
Operating Segment Reporting
Production costs applicable to sales	(6,245)	(4,423)	(18,117)	(11,761)
Exploration | United States Reportable Segment [Member]
Operating Segment Reporting
Production costs applicable to sales	(1,432)	(2,395)	(3,887)	(5,235)
Exploration | Canada
Operating Segment Reporting
Production costs applicable to sales	(4,817)	(1,189)	(12,532)	(4,434)
Exploration | Mexico Reportable Segment [Member]
Operating Segment Reporting
Production costs applicable to sales	$ 4	(427)	(14)	(463)
Exploration | Los Azules
Operating Segment Reporting
Production costs applicable to sales		$ (412)	$ (1,684)	$ (1,629)