Income and Mining Taxes - Reconciliation of Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income and mining tax (expense) benefit at statutory rate	$ (13,161)	$ 75,185	$ 14,052
State tax provision from continuing operations	(152)	1,243	2,284
Change in valuation allowance	(17,522)	(77,220)	2,471
Percentage depletion	5,056	820	89
Uncertain tax positions	2,321	2,358	1,830
U.S. and foreign permanent differences	3,844	2,272	3,314
Foreign exchange rates	1,390	(7,066)	(3,973)
Foreign inflation and indexing	684	(2,933)	(2,374)
Foreign tax rate differences	(3,971)	19,729	(24)
Mining, foreign withholding, and other taxes	(17,457)	(2,746)	(3,857)
Other, net	1,923	(513)	2,968
Income and mining tax benefit (expense)	$ 37,045	$ (11,129)	$ (16,780)