Income and Mining Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Contingency [Line Items]
Tax (expense) benefit	$ 37,045	$ (11,129)	$ (16,780)
Unrecognized Tax Benefits	700	2,700	3,800
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	1,100	$ 2,300	$ 3,500
Minimum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	500
Maximum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	$ 1,500