Income and Mining Taxes - Reconciliation of Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income and mining tax (expense) benefit at statutory rate		$ 14,052	$ (14,037)	$ 3,718
State tax provision from continuing operations		2,284	26	336
Change in valuation allowance		2,471	86,712	40,517
Effect of tax legislation		0	(88,174)	0
Percentage depletion		89	703	983
Uncertain tax positions		1,830	2,596	(8,829)
U.S. and foreign permanent differences		3,314	2,348	(2,652)
Foreign exchange rates		(3,973)	(14,180)	19,701
Foreign inflation and indexing		(2,374)	(2,346)	(670)
Foreign tax rate differences		(24)	2,929	120
Mining, foreign withholding, and other taxes		(3,857)	(11,274)	(11,052)
Other, net		2,968	5,699	0
Legal entity reorganization		0	0	$ (8,925)
Income and mining tax benefit (expense)	$ (16,780)	$ 28,998	$ (33,247)