INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE - Changes in Company's Investment in MSC (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Change in the investment in MSC
Investment in MSC, beginning of period			$ 127,814
Income tax recovery	$ (501)	$ (2,140)	(383)	$ (3,278)
Dividend distribution received			(2,020)	(7,231)
Investment in MSC, end of period	119,347		119,347		$ 127,814
MSC
Change in the investment in MSC
Investment in MSC, beginning of period			127,814	150,064	150,064
Attributable net loss from MSC	(1,784)	(3,773)	(3,142)	(3,343)	(10,065)
Amortization of fair value increments	(2,459)	(2,482)	(4,372)	(4,597)	(9,730)
Income tax recovery	106	$ 3,990	1,067	$ 5,463	7,930
Dividend distribution received			(2,020)		(10,385)
Investment in MSC, end of period	$ 119,347		$ 119,347		$ 127,814