Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Changes in Benefit Obligation and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Funded status:
Current assets	$ 49,618	$ 41,938
CWP Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	161,878	170,014
State administrative fees and insurance bond premiums	0	0	$ 0
Service cost	7,812	2,985	2,313
Interest cost	14,462	8,264	8,285
Benefit obligations assumed in Merger	118,585	0
Actuarial loss (gain)	11,293	(2,145)
Benefits paid	(28,290)	(17,240)
Benefit obligation at end of period	285,740	161,878	170,014
Funded status:
Current assets	0	0
Current liabilities	(24,539)	(16,389)
Noncurrent liabilities	(261,201)	(145,489)
Net asset (obligation) recognized	(285,740)	(161,878)
Amounts recognized in accumulated other comprehensive (loss) income consist of:
Net actuarial loss (gain)	12,761	1,638
Net amount recognized (before tax effect)	12,761	1,638
Workers’ Compensation
Change in benefit obligation:
Benefit obligation at beginning of period	46,107	48,153
State administrative fees and insurance bond premiums	1,730	1,837	1,953
Service cost	6,912	5,857	5,597
Interest cost	2,220	2,289	2,514
Benefit obligations assumed in Merger	0	0
Actuarial loss (gain)	1,521	1,203
Benefits paid	(11,682)	(13,232)
Benefit obligation at end of period	46,808	46,107	$ 48,153
Funded status:
Current assets	766	1,000
Current liabilities	(12,611)	(11,056)
Noncurrent liabilities	(34,963)	(36,051)
Net asset (obligation) recognized	(46,808)	(46,107)
Amounts recognized in accumulated other comprehensive (loss) income consist of:
Net actuarial loss (gain)	(18,874)	(22,234)
Net amount recognized (before tax effect)	$ (18,874)	$ (22,234)