Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 1,200
Concentrate Sales Contracts
Derivative [Line Items]
Provisional gain (loss) on derivatives and commodity contracts	959	$ 337	$ 111
Interest rate swap
Derivative [Line Items]
Net derivative gain (loss)	0	$ (178)	$ (60)
Designated as Hedging Instrument | Gold zero cost collars
Derivative [Line Items]
After tax gains in AOCI	11,100
Payments of novation funding costs	$ 3,800