Discontinued Operations - Details of ESM Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
ARO liabilities transferred	$ 203,137	$ 165,064	$ 192,038
Eagle Specialty Materials, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash	90,000
DIP obligation	3,008
Other	331
Total consideration	93,339
Gain on sale	(59,543)
Eagle Butte and Belle Ayr Mines | Eagle Specialty Materials, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
ARO liabilities transferred	$ 152,882