INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE - Summary of Operating Results from MSC (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Net Sales	$ 15,640	$ 41,285	$ 41,285
Other operating expenses	(12,967)	(19,298)
Net (loss) income before tax	(10,018)	(6,349)
Net (loss) income	(10,136)	(5,211)
Income tax recovery	118	(1,138)
(Loss) from investment in MSC, net of amortization	(2,310)	(212)
MSC
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Net Sales	46,203	50,662
Cost of goods and services sold	(36,340)	(43,468)
Other operating expenses	(9,403)	(4,059)
Other (expenses) income	(2,443)	(2,118)
Net (loss) income before tax	(1,983)	1,017
Current and deferred tax expense	(789)	(139)
Net (loss) income	$ (2,772)	878
MSC
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Ownership interest (as a percent)	49.00%
Net income (loss)	$ (1,358)	430	(10,065)
Amortization of fair value increments	(1,913)	(2,115)	(9,730)
Income tax recovery	961	1,473	$ 7,930
(Loss) from investment in MSC, net of amortization	$ (2,310)	$ (212)
Corporate Venture
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Ownership interest (as a percent)	100.00%