Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Changes in Accumulated Postemployment Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Funded status:
Current assets	$ 41,938	$ 47,246
CWP Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	170,014	161,113
State administrative fees and insurance bond premiums	0	0	$ 0
Service cost	2,985	2,313	2,905
Interest cost	8,264	8,285	5,060
Actuarial (gain) loss	(2,145)	13,270
Benefits and other payments	(17,240)	(14,967)
Benefit obligation at end of period	161,878	170,014	161,113
Funded status:
Current assets	0	0
Current liabilities	(16,389)	(15,071)
Noncurrent liabilities	(145,489)	(154,943)
Net asset (obligation) recognized	(161,878)	(170,014)
Amounts recognized in accumulated other comprehensive (loss) income consist of:
Net actuarial loss (gain)	1,638	4,217
Net amount recognized (before tax effect)	1,638	4,217
Workers Compensation
Change in benefit obligation:
Benefit obligation at beginning of period	48,153	50,344
State administrative fees and insurance bond premiums	1,837	1,953	1,817
Service cost	5,857	5,597	4,920
Interest cost	2,289	2,514	1,369
Actuarial (gain) loss	1,203	(2,919)
Benefits and other payments	(13,232)	(9,336)
Benefit obligation at end of period	46,107	48,153	$ 50,344
Funded status:
Current assets	1,000	1,010
Current liabilities	(11,056)	(10,019)
Noncurrent liabilities	(36,051)	(39,144)
Net asset (obligation) recognized	(46,107)	(48,153)
Amounts recognized in accumulated other comprehensive (loss) income consist of:
Net actuarial loss (gain)	(22,234)	(25,597)
Net amount recognized (before tax effect)	$ (22,234)	$ (25,597)