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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
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Net Sales													$ 128,822	$ 67,724	$ 60,388
Other operating expenses													(82,035)	(48,571)	(16,908)
(Loss) income before income and mining taxes													(47,640)	(26,003)	17,306
Net income	$ (20,989)	$ (13,290)	$ (5,380)	$ (5,211)	$ 2,169	$ (8,072)	$ (1,712)	$ (3,018)	$ (4,491)	$ 4,208	$ 8,353	$ 12,985	(44,870)	(10,634)	21,055
Income tax recovery													(2,770)	(15,369)	(3,749)
(Loss) from investment in MSC, net of amortization													(11,865)	(44)	12,951
MSC
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Cost of goods and services sold													(178,089)	(177,180)	(173,679)
Other operating expenses													(21,083)	(20,956)	(21,770)
Other (expenses) income													(15,801)	(15,657)	10,425
(Loss) income before income and mining taxes													(9,607)	13,300	50,937
Current & deferred taxes													(10,934)	(18,050)	(18,363)
Net sales													205,366	227,093	235,961
Net (loss) income													$ (20,541)	$ (4,750)	$ 32,574
MSC
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Ownership interest (as a percent)	49.00%				49.00%				49.00%				49.00%	49.00%	49.00%
Net income (loss)													$ (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
(Loss) from investment in MSC, net of amortization													$ (11,865)	$ (44)	$ 12,951
Corporate Venture
INVESTMENT IN MINERA SANTA CRUZ S.A. ("MSC") - SAN JOSE MINE
Ownership interest (as a percent)	100.00%				100.00%				100.00%				100.00%	100.00%	100.00%