Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	$ 8,603,814	$ 5,764,081
Less: Accumulated Depreciation, Depletion and Amortization	4,213,432	3,842,382
Total Property, Plant and Equipment - Net	4,390,382	1,921,699
Plant and Equipment
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	4,774,817	3,633,741
Coal Properties and Surface Lands
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	2,225,310	913,819
Airshafts
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	592,493	521,334
Mine Development
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	673,946	366,260
Advance Mining Royalties
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	$ 337,248	$ 328,927