Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	$ 5,408,577	$ 5,250,805
Less—Accumulated Depreciation, Depletion and Amortization	3,448,495	3,272,255
Total Property, Plant and Equipment—Net	1,960,082	1,978,550
Plant and Equipment
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	3,330,755	3,209,232
Coal Properties and Surface Lands
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	898,628	881,551
Airshafts
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	481,090	473,866
Mine Development
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	366,241	357,479
Advance Mining Royalties
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	$ 331,863	$ 328,677