Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
CWP Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,905	$ 4,460	$ 4,603
Interest cost	5,060	4,710	6,206
Recognized net actuarial loss	4,238	8,364	5,604
State administrative fees and insurance bond premiums	0	0	0
Net periodic benefit (credit) cost	12,203	17,534	16,413
Workers Compensation
Defined Benefit Plan Disclosure [Line Items]
Service cost	4,920	4,236	6,276
Interest cost	1,369	1,127	1,844
Recognized net actuarial loss	(420)	(179)	(488)
State administrative fees and insurance bond premiums	1,817	1,778	1,996
Net periodic benefit (credit) cost	$ 7,686	$ 6,962	$ 9,628