INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE - Summary of Operating Results from MSC (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Revenue from gold and silver sales	$ 32,691	$ 26,896	$ 84,657	$ 101,743
Other operating expenses	(19,399)	(21,219)	(47,251)	(58,286)
Net income (loss)	(13,657)	(14,903)	(37,190)	(28,772)
Net income (loss)	(11,465)	(13,290)	(34,615)	(23,881)
Income tax recovery	(2,192)	(1,613)	(2,575)	(4,891)
(Loss) from investment in MSC, net of amortization	(328)	(4,973)	(6,775)	(7,450)
Dividends received				9,400
MSC
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Net loss	803	(5,164)	(2,339)	(8,506)	$ (10,065)
Amortization of fair value increments	(2,551)	(2,537)	(6,923)	(7,135)	(9,730)
Income tax recovery	$ 1,420	2,728	$ 2,487	8,191	$ 7,930
Ownership interest (as a percent)	49.00%		49.00%
(Loss) from investment in MSC, net of amortization	$ (328)	(4,973)	$ (6,775)	(7,450)
Dividends received	2,000	2,100	4,000
MSC
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Revenue from gold and silver sales	70,908	47,814	179,708	150,748
Cost of goods and services sold	(51,238)	(48,193)	(140,474)	(135,007)
Other operating expenses	(8,221)	(5,164)	(27,064)	(12,776)
Other expenses	(5,298)	(4,106)	(8,596)	(12,360)
Net income (loss)	6,151	(9,649)	3,574	(9,395)
Current and deferred tax expense	(4,512)	(889)	(8,350)	(7,965)
Net income (loss)	$ 1,639	$ (10,538)	$ (4,776)	$ (17,360)
Summarized key financial information (as a percent)			100.00%