Components of Coal Workers' Pneumoconiosis and Workers' Compensation Net Periodic Benefit Costs - Components of Net Period Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
CWP
Defined Contribution Plan Disclosure [Line Items]
Service Cost	$ 578	$ 726
Interest Cost	2,071	1,265
Amortization of Actuarial Loss	(261)	1,060
State Administrative Fees and Insurance Bond Premiums	0	0
Net Periodic Benefit (Credit) Cost	2,388	3,051
Workers' Compensation
Defined Contribution Plan Disclosure [Line Items]
Service Cost	1,399	1,230
Interest Cost	628	342
Amortization of Actuarial Loss	(512)	(105)
State Administrative Fees and Insurance Bond Premiums	545	437
Net Periodic Benefit (Credit) Cost	$ 2,060	$ 1,904