Income and Mining Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Income Tax Contingency [Line Items]
Tax (expense) benefit	$ (3,939)	$ (8,658)
Effective Income Tax Rate Reconciliation, Percent	(24.90%)	25.80%
Unrecognized Tax Benefits	$ 700		$ 2,700
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	900		$ 2,300
Minimum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	500
Maximum
Income Tax Contingency [Line Items]
Unrecognized income tax liability	$ 1,500