Segment Information - Reconciliation segment income to net income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Information
Net Income (Loss)	$ 464,038	$ 1,330,914	$ 337,573
Provision for (benefit from) income taxes	87,514	(251,926)	1,874
Interest expense, net	(2,438)	13,162	23,344
Depreciation, depletion and amortization	146,418	133,300	120,327
Accretion on asset retirement obligation	21,170	17,721	21,748
Loss on divestitures			24,225
Non-service related pension and postretirement benefit (credits) costs	(3,786)	2,841	4,339
Net loss resulting from early retirement of debt	1,126	14,420
Adjusted EBITDA	714,042	1,260,432	533,430
EBITDA from idled or otherwise disposed operations	15,986	(828)	2,469
Selling, general and administrative expenses	98,871	105,355	92,342
Other	14,404	10,857	(9,702)
Segment Adjusted EBITDA from coal operations	$ 843,303	$ 1,375,816	$ 618,539