OPERATING SEGMENT REPORTING - Summary of Reportable Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Segment Reporting
Revenue from gold and silver sales	$ 23,740	$ 31,400
Depreciation and depletion	(5,137)	(6,698)
Gross (loss) profit	(4,986)	(3,685)
Advanced projects	(1,799)	(2,550)
Impairment of mineral property interests and plant and equipment (Note 8)		(83,805)
Loss from investment in Minera Santa Cruz S.A.	(574)	(2,676)
Segment loss	(12,315)	(96,506)
General and Administrative and other	(2,166)	(3,779)
Loss before income and mining taxes	(14,481)	(100,285)
Capital expenditures	10,324	5,536
USA
Operating Segment Reporting
Depreciation and depletion	(1,741)	(3,862)
Gross (loss) profit	(2,405)	(6,577)
Advanced projects	(84)	(366)
Impairment of mineral property interests and plant and equipment (Note 8)		(83,805)
Segment loss	(3,353)	(91,557)
Capital expenditures	757	1,807
Canada
Operating Segment Reporting
Depreciation and depletion	(3,395)	(2,748)
Gross (loss) profit	(1,490)	2,784
Advanced projects	(623)	(1,066)
Segment loss	(5,547)	(687)
Capital expenditures	9,567	3,729
Mexico
Operating Segment Reporting
Depreciation and depletion	(1)	(88)
Gross (loss) profit	(1,091)	108
Advanced projects	(1,092)	(1,118)
Segment loss	(2,191)	(1,010)
MSC
Operating Segment Reporting
Loss from investment in Minera Santa Cruz S.A.	(574)	(2,676)
Segment loss	(574)	(2,676)
Los Azules
Operating Segment Reporting
Segment loss	(650)	(576)
Gold and silver sales
Operating Segment Reporting
Revenue from gold and silver sales	23,740	31,400
Gold and silver sales | USA
Operating Segment Reporting
Revenue from gold and silver sales	12,893	14,317
Gold and silver sales | Canada
Operating Segment Reporting
Revenue from gold and silver sales	8,561	12,739
Gold and silver sales | Mexico
Operating Segment Reporting
Revenue from gold and silver sales	2,286	4,344
Production costs applicable to sales
Operating Segment Reporting
Production costs applicable to sales	(23,589)	(28,387)
Production costs applicable to sales | USA
Operating Segment Reporting
Production costs applicable to sales	(13,557)	(17,032)
Production costs applicable to sales | Canada
Operating Segment Reporting
Production costs applicable to sales	(6,656)	(7,207)
Production costs applicable to sales | Mexico
Operating Segment Reporting
Production costs applicable to sales	(3,376)	(4,148)
Exploration
Operating Segment Reporting
Production costs applicable to sales	(4,956)	(3,790)
Exploration | USA
Operating Segment Reporting
Production costs applicable to sales	(864)	(809)
Exploration | Canada
Operating Segment Reporting
Production costs applicable to sales	(3,434)	(2,405)
Exploration | Mexico
Operating Segment Reporting
Production costs applicable to sales	(8)
Exploration | Los Azules
Operating Segment Reporting
Production costs applicable to sales	$ (650)	$ (576)