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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
CWP
Defined Contribution Plan Disclosure [Line Items]
Service Cost	$ 578	$ 726	$ 1,156	$ 1,452
Interest Cost	2,072	1,265	4,143	2,530
Amortization of Actuarial Loss	(262)	1,059	(523)	2,119
State Administrative Fees and Insurance Bond Premiums	0	0	0	0
Net Periodic Benefit (Credit) Cost	2,388	3,050	4,776	6,101
Workers' Compensation
Defined Contribution Plan Disclosure [Line Items]
Service Cost	1,399	1,230	2,798	2,460
Interest Cost	629	342	1,257	684
Amortization of Actuarial Loss	(513)	(105)	(1,025)	(210)
State Administrative Fees and Insurance Bond Premiums	466	448	1,011	885
Net Periodic Benefit (Credit) Cost	$ 1,981	$ 1,915	$ 4,041	$ 3,819