INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE - Changes in Company's Investment in MSC (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in the investment in MSC
Investment in MSC, beginning balance	$ 150,064
Income tax recovery	(2,770)	$ (15,369)	$ (3,749)
Distributions received	(10,385)	(12,212)	(17,738)
Investment in MSC, ending balance	127,814	150,064
MSC
Change in the investment in MSC
Investment in MSC, beginning balance	150,064	162,320
Attributable net income (loss) from MSC	(10,065)	(2,328)	15,961
Amortization of fair value increments	(9,730)	(9,632)	(12,274)
Income tax recovery	7,930	11,916	9,264
Distributions received	(10,385)	(12,212)
Investment in MSC, ending balance	$ 127,814	$ 150,064	$ 162,320