Segment Information - Schedule of operating segment results (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) item	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of distinct lines of business | item			2
Revenues	$ 863,835	$ 594,412	$ 2,865,129	$ 1,402,345
Adjusted EBITDA	222,956	131,595	1,003,906	229,018
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
Total assets	2,319,862	1,930,949	2,319,862	1,930,949	$ 2,117,160
Capital expenditures	41,360	64,089	94,517	212,046
Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	444,306	295,291	1,640,970	693,522
Adjusted EBITDA	155,185	118,548	810,615	221,391
Depreciation, depletion and amortization	28,354	25,041	82,738	68,577
Accretion on asset retirement obligation	553	508	1,660	1,523
Total assets	1,020,849	965,252	1,020,849	965,252
Capital expenditures	36,389	61,504	79,896	204,347
Operating Segments | Thermal
Segment Reporting Information [Line Items]
Revenues	419,529	299,096	1,224,159	707,394
Adjusted EBITDA	96,812	52,737	290,648	107,589
Depreciation, depletion and amortization	5,388	5,488	15,554	15,170
Accretion on asset retirement obligation	3,444	4,419	10,331	13,256
Total assets	325,580	193,060	325,580	193,060
Capital expenditures	4,604	507	13,200	1,370
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	0	25	0	1,429
Adjusted EBITDA	(29,041)	(39,690)	(97,357)	(99,962)
Depreciation, depletion and amortization	216	231	656	694
Accretion on asset retirement obligation	433	510	1,299	1,532
Total assets	973,433	772,637	973,433	772,637
Capital expenditures	$ 367	$ 2,078	$ 1,421	$ 6,329