Income and Mining Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Tax Contingency [Line Items]
Tax (expense) benefit	$ 13,113	$ 218	$ 12,018	$ (13,986)
Effective Income Tax Rate Reconciliation, Percent	(32.80%)			1.60%
Unrecognized Tax Benefits	$ 600		600		$ 2,700
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	1,000		1,000		$ 2,300
Minimum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	500		500
Maximum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	$ 1,500		$ 1,500