Derivative Financial Instruments - Summary of Pre-tax Gains (Losses) On Derivatives Designated as Cash Flow Hedges (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gains (losses) recognized in OCI - effective portion:	$ (7,097)	$ 0	$ (6,891)	$ 0
Gains (losses) reclassified from AOCI into net income - effective portion:	(679)	0	(679)	0
Gold zero cost collars
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gains (losses) recognized in OCI - effective portion:	(14,490)	0	(14,349)	0
Gains (losses) reclassified from AOCI into net income - effective portion:	0	0	0	0
Foreign Exchange Forward
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gains (losses) recognized in OCI - effective portion:	7,393	0	7,458	0
Gains (losses) reclassified from AOCI into net income - effective portion:	$ (679)	$ 0	$ (679)	$ 0