Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred Tax Asset:
Asset retirement obligations	$ 40,445	$ 41,400
Postretirement benefits other than pensions	40,226	47,730
Pneumoconiosis benefits	31,663	33,867
Other	44,735	28,280
Total Deferred Tax Asset	157,069	151,277
Deferred Tax Liability:
Equity Partnerships	(155,039)	(122,220)
Property, plant and equipment	(39,154)	(52,409)
Other	(12,090)	(12,867)
Total Deferred Tax Liability	(206,283)	(187,496)
Net Deferred Tax Liability	$ (49,214)	$ (36,219)