Segment Information - Reconciliation segment income to net income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Information
Net Income (Loss)	$ 77,353	$ 407,563	$ 275,461	$ 679,435
Provision for income taxes	12,920	496	50,058	951
Interest expense, net	(664)	4,610	126	11,633
Depreciation, depletion and amortization	36,077	32,780	71,556	64,990
Accretion on asset retirement obligation	5,293	4,430	10,585	8,860
Non-service related pension and postretirement benefit (credits) costs	(593)	459	(1,185)	1,332
Net loss resulting from early retirement of debt		9,629	1,126	13,749
Adjusted EBITDA	130,386	459,967	407,727	780,950
EBITDA from idled or otherwise disposed operations	4,664	3,957	8,696	6,348
Selling, general and administrative expenses	22,791	26,516	48,813	53,164
Other	4,177	(678)	6,094	8,804
Segment Adjusted EBITDA from coal operations	$ 162,018	$ 489,762	$ 471,330	$ 849,266