Components of Coal Workers' Pneumoconiosis (CWP) and Workers' Compensation Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
CWP
Defined Contribution Plan Disclosure [Line Items]
Service Cost	$ 2,003	$ 746	$ 5,809	$ 2,239
Interest Cost	3,687	2,066	10,776	6,198
Amortization of Actuarial Loss (Gain)	42	109	127	326
Fees, Premiums and Assessments	0	0	0	0
Net Periodic Benefit Cost	5,732	2,921	16,712	8,763
Workers' Compensation
Defined Contribution Plan Disclosure [Line Items]
Service Cost	1,728	1,465	5,184	4,393
Interest Cost	555	572	1,665	1,717
Amortization of Actuarial Loss (Gain)	(460)	(540)	(1,380)	(1,620)
Fees, Premiums and Assessments	2,273	464	6,383	1,393
Net Periodic Benefit Cost	$ 4,096	$ 1,961	$ 11,852	$ 5,883