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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
CWP
Defined Contribution Plan Disclosure [Line Items]
Service Cost	$ 746	$ 578	$ 2,239	$ 1,734
Interest Cost	2,066	2,071	6,198	6,214
Amortization of Actuarial Loss (Gain)	109	(261)	326	(784)
State Administrative Fees and Insurance Bond Premiums	0	0	0	0
Net Periodic Benefit Cost (Credit)	2,921	2,388	8,763	7,164
Workers' Compensation
Defined Contribution Plan Disclosure [Line Items]
Service Cost	1,465	1,400	4,393	4,198
Interest Cost	572	628	1,717	1,885
Amortization of Actuarial Loss (Gain)	(540)	(512)	(1,620)	(1,537)
State Administrative Fees and Insurance Bond Premiums	464	471	1,393	1,482
Net Periodic Benefit Cost (Credit)	$ 1,961	$ 1,987	$ 5,883	$ 6,028