Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
CWP Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7,812	$ 2,985	$ 2,313
Interest cost	14,462	8,264	8,285
Recognized net actuarial loss (gain)	170	434	(1,045)
State administrative fees and insurance bond premiums	0	0	0
Net periodic benefit cost (credit)	22,444	11,683	9,553
Workers’ Compensation
Defined Benefit Plan Disclosure [Line Items]
Service cost	6,912	5,857	5,597
Interest cost	2,220	2,289	2,514
Recognized net actuarial loss (gain)	(1,839)	(2,160)	(2,049)
State administrative fees and insurance bond premiums	1,730	1,837	1,953
Net periodic benefit cost (credit)	9,023	7,823	8,015
Insured workers’ compensation fees and assessments	6,407	0	0
Total workers’ compensation expense	$ 15,430	$ 7,823	$ 8,015