Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Changes in Accumulated Postemployment Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in benefit obligation:
Current assets	$ 47,246	$ 38,548
CWP Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	161,113	215,871
State administrative fees and insurance bond premiums	0	0	$ 0
Service cost	2,313	2,905	4,460
Interest cost	8,285	5,060	4,710
Actuarial loss (gain)	13,270	(46,498)
Benefits and other payments	(14,967)	(16,225)
Benefit obligation at end of period	170,014	161,113	215,871
Current assets	0	0
Current liabilities	(15,071)	(12,723)
Noncurrent liabilities	(154,943)	(148,390)
Net asset (obligation) recognized	(170,014)	(161,113)
Net actuarial loss (gain)	4,217	(10,098)
Net amount recognized (before tax effect)	4,217	(10,098)
Workers Compensation
Change in benefit obligation:
Benefit obligation at beginning of period	50,344	67,261
State administrative fees and insurance bond premiums	1,953	1,817	1,778
Service cost	5,597	4,920	4,236
Interest cost	2,514	1,369	1,127
Actuarial loss (gain)	(2,919)	(14,422)
Benefits and other payments	(9,336)	(10,601)
Benefit obligation at end of period	48,153	50,344	$ 67,261
Current assets	1,010	1,058
Current liabilities	(10,019)	(10,451)
Noncurrent liabilities	(39,144)	(40,951)
Net asset (obligation) recognized	(48,153)	(50,344)
Net actuarial loss (gain)	(25,597)	(24,727)
Net amount recognized (before tax effect)	$ (25,597)	$ (24,727)