Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Deferred Tax Asset:
Postretirement benefits other than pensions	$ 47,730,000	$ 56,119,000
Asset retirement obligations	41,400,000	44,680,000
Pneumoconiosis benefits	33,867,000	33,946,000
Compensation	8,317,000	8,826,000
Workers' compensation	6,461,000	7,099,000
State bonus, net of Federal	1,917,000	2,973,000
Long-term disability	1,280,000	1,463,000
Operating lease liability	1,033,000	46,000
Net operating loss	238,000	211,000
Financing	124,000	838,000
Other	8,910,000	4,957,000
Total Deferred Tax Asset	151,277,000	161,158,000
Valuation Allowance	0	0
Net Deferred Tax Asset	151,277,000	161,158,000
Deferred Tax Liability:
Equity Partnerships	(122,220,000)	(118,231,000)
Property, plant and equipment	(52,409,000)	(54,322,000)
Advance mining royalties	(6,476,000)	(6,782,000)
Salary retirement	(5,468,000)	(3,737,000)
Right of use assets	(923,000)	0
Total Deferred Tax Liability	(187,496,000)	(183,072,000)
Net Deferred Tax Liability	$ (36,219,000)	$ (21,914,000)