Components of Coal Workers' Pneumoconiosis (CWP) and Workers' Compensation Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
CWP
Defined Contribution Plan Disclosure [Line Items]
Service Cost	$ 1,690	$ 1,816
Interest Cost	3,382	3,419
Recognized Net Actuarial Loss (Gain)	317	42
State Administrative Fees and Insurance Bond Premiums	0	0
Net Periodic Benefit Cost	5,389	5,277
Workers' Compensation
Defined Contribution Plan Disclosure [Line Items]
Service Cost	3,195	1,728
Interest Cost	501	555
Recognized Net Actuarial Loss (Gain)	(356)	(460)
State Administrative Fees and Insurance Bond Premiums	766	390
Net Periodic Benefit Cost	4,106	2,213
Insured Workers’ Compensation Fees and Assessments	519	1,346
Total Workers’ Compensation Expense	$ 4,625	$ 3,559