Income and Mining Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Income Tax Contingency [Line Items]
Tax (expense) benefit	$ 12,786	$ (3,939)
Effective Income Tax Rate Reconciliation, Percent	(86.10%)	(24.90%)
Unrecognized Tax Benefits	$ 300		$ 700
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	300		$ 1,100
Minimum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	500
Maximum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	$ 1,000