Coal Workers' Pneumoconiosis and Workers' Compensation - Schedule of Changes in Accumulated Postemployment Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Change in benefit obligation:
Current assets	$ 38,548	$ 38,947
CWP Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	215,871	241,923
State administrative fees and insurance bond premiums	0	0	$ 0
Service cost	2,905	4,460	4,603
Interest cost	5,060	4,710	6,206
Actuarial gain	(46,498)	(22,256)
Benefits and other payments	(16,225)	(12,966)
Benefit obligation at end of period	161,113	215,871	241,923
Current assets	0	0
Current liabilities	(12,723)	(12,398)
Noncurrent liabilities	(148,390)	(203,473)
Net asset (obligation) recognized	(161,113)	(215,871)
Net actuarial loss (gain)	(10,098)	40,638
Net amount recognized (before tax effect)	(10,098)	40,638
Workers Compensation
Change in benefit obligation:
Benefit obligation at beginning of period	67,261	73,441
State administrative fees and insurance bond premiums	1,817	1,778	1,996
Service cost	4,920	4,236	6,276
Interest cost	1,369	1,127	1,844
Actuarial gain	(14,422)	(2,039)
Benefits and other payments	(10,601)	(11,282)
Benefit obligation at end of period	50,344	67,261	$ 73,441
Current assets	1,058	1,092
Current liabilities	(10,451)	(10,205)
Noncurrent liabilities	(40,951)	(58,148)
Net asset (obligation) recognized	(50,344)	(67,261)
Net actuarial loss (gain)	(24,727)	(10,726)
Net amount recognized (before tax effect)	$ (24,727)	$ (10,726)