Other, Net - Summary of Pre-development, reclamation and other (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Income and Expenses [Abstract]
Accretion Expense, Including Asset Retirement Obligations	$ 11,754	$ 12,154	$ 11,116
Other Operating Income (Expense), Net	4,954	6,267	8,927
Gain (Loss) on Termination of Lease	(4,051)	0	0
Covid-19 Related Costs	15,414	0	0
Care and maintenance costs	17,082	0	0
Temporary Suspension Costs	10,501	0	0
Pre-development, reclamation, and other	$ 55,654	$ 18,421	$ 20,043