Segment Information - Reconciliation segment income to net income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Information
Net income (loss)	$ 1,330,914	$ 337,573	$ (344,615)
(Benefit from) provision for income taxes	(251,926)	1,874	(7)
Interest expense, net	13,162	23,344	10,624
Depreciation, depletion and amortization	133,300	120,327	121,552
Accretion on asset retirement obligation	17,721	21,748	19,887
Costs related to proposed joint venture with Peabody Energy			16,087
Asset impairment and restructuring			221,380
Gain on property insurance recovery related to Mountain Laurel longwall			(23,518)
Loss (Gain) on divestitures		24,225	(1,505)
Non-service related pension and postretirement benefit costs	2,841	4,339	3,884
Net loss resulting from early retirement of debt	14,420
Reorganization items, net			(26)
Adjusted EBITDA	1,260,432	533,430	23,743
EBITDA from idled or otherwise disposed operations	(828)	2,469	15,858
Selling, general and administrative expenses	105,355	92,342	82,397
Other	10,857	(9,702)	3,359
Segment Adjusted EBITDA from coal operations	$ 1,375,816	$ 618,539	$ 125,357