Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
CWP Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,985	$ 2,313	$ 2,905
Interest cost	8,264	8,285	5,060
Recognized net actuarial loss (gain)	434	(1,045)	4,238
State administrative fees and insurance bond premiums	0	0	0
Net periodic benefit cost (credit)	11,683	9,553	12,203
Workers Compensation
Defined Benefit Plan Disclosure [Line Items]
Service cost	5,857	5,597	4,920
Interest cost	2,289	2,514	1,369
Recognized net actuarial loss (gain)	(2,160)	(2,049)	(420)
State administrative fees and insurance bond premiums	1,837	1,953	1,817
Net periodic benefit cost (credit)	$ 7,823	$ 8,015	$ 7,686