Income and Mining Taxes - Reconciliation of Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income and mining tax (expense) benefit at statutory rate	$ (14,037)	$ 3,718	$ 110,848
State tax provision from continuing operations	26	336	(2,075)
Change in valuation allowance	86,712	40,517	(70,457)
Effect of tax legislation	(88,174)	0	0
Percentage depletion	703	983	0
Uncertain tax positions	2,596	(8,829)	170
U.S. and foreign permanent differences	2,348	(2,652)	(3,376)
Mineral interest related	0	0	(18,318)
Foreign exchange rates	(14,180)	19,701	21,461
Foreign inflation and indexing	(2,346)	(670)	1,117
Foreign tax rate differences	2,929	120	(14,062)
Mining, foreign withholding, and other taxes	(11,274)	(11,052)	8,141
Other, net	5,699	0	(4,374)
Legal entity reorganization	0	(8,925)	0
Income and mining tax benefit (expense)	$ 28,998	$ (33,247)	$ (29,075)