Income and Mining Taxes - Income (Loss) Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Examination [Line Items]
United States, Income (loss) before tax	$ 40,890	$ (16,702)	$ (50,522)
Foreign, Income (loss) before tax	21,782	(341,323)	(15,213)
Total	62,672	(358,025)	(65,735)
Tax (expense) benefit	$ 37,045	$ (11,129)	$ (16,780)