Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Deferred Tax Asset:
Net operating loss	$ 222,317	$ 1,097
Pneumoconiosis benefits	59,729	31,663
Postretirement benefits other than pensions	44,587	40,226
Asset retirement obligations	43,406	40,445
Other	55,568	43,638
Total Deferred Tax Asset	425,607	157,069
Valuation Allowance	(75,338)	0
Net Deferred Tax Asset	350,269	157,069
Deferred Tax Liability:
Equity Partnerships	(410,966)	(155,039)
Property, plant and equipment	(54,626)	(39,154)
Other	(14,790)	(12,090)
Total Deferred Tax Liability	(480,382)	(206,283)
Net Deferred Tax Liability	$ (130,113)	$ (49,214)