Segment Information - Reconciliation segment income to net income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Information
Net income	$ 181,007	$ 89,143	$ 860,443	$ 110,967
Provision for (benefit from) income taxes	474	(1,082)	1,424	1,301
Interest expense, net	1,836	6,151	13,469	12,746
Depreciation, depletion and amortization	33,958	30,760	98,948	84,441
Accretion on asset retirement obligation	4,430	5,437	13,290	16,311
Non-service related pension and postretirement benefit costs	857	1,186	2,189	3,252
Net loss resulting from early retirement of debt	394		14,143
Adjusted EBITDA	222,956	131,595	1,003,906	229,018
EBITDA from idled or otherwise disposed operations	3,624	3,074	9,972	10,637
Selling, general and administrative expenses	26,107	21,081	79,271	66,679
Other	(690)	15,535	8,114	22,646
Segment Adjusted EBITDA from coal operations	$ 251,997	$ 171,285	$ 1,101,263	$ 328,980