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OPERATING SEGMENT REPORTING - Geographic information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Operating Segment Reporting
Revenue from gold and silver sales	$ 31,400	$ 15,583
Long-lived Assets	449,558		$ 539,150
Investment in MSC	107,507		110,183
Lease assets	900
MSC
Operating Segment Reporting
Revenue from gold and silver sales	37,390	47,885
Investment in MSC	107,507		110,183	$ 127,814
United States
Operating Segment Reporting
Revenue from gold and silver sales	14,317	842
Long-lived Assets	50,599		135,854
Canada
Operating Segment Reporting
Revenue from gold and silver sales	12,739	8,943
Long-lived Assets	78,505		77,147
Mexico
Operating Segment Reporting
Revenue from gold and silver sales	4,344	$ 5,798
Long-lived Assets	21,457		23,551
Argentina
Operating Segment Reporting
Long-lived Assets	298,997		302,598
Argentina \| MSC
Operating Segment Reporting
Investment in MSC	$ 107,500		$ 110,200