Segment Information - Schedule of operating segment results (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) item	Sep. 30, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of distinct lines of business | item			2
Revenues	$ 617,899	$ 744,601	$ 1,906,840	$ 2,371,826
Adjusted EBITDA	44,161	126,291	206,983	534,018
Depreciation, depletion and amortization	40,890	36,717	118,149	108,273
Accretion on asset retirement obligation	5,869	5,292	17,608	15,877
Capital expenditures	34,522	44,424	126,888	121,030
Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	361,916	432,835	1,154,938	1,420,758
Adjusted EBITDA	54,167	128,322	270,978	524,218
Depreciation, depletion and amortization	32,702	29,494	95,181	85,575
Accretion on asset retirement obligation	647	651	1,942	1,880
Capital expenditures	23,438	33,806	94,603	94,205
Operating Segments | Thermal
Segment Reporting Information [Line Items]
Revenues	255,983	311,766	751,902	951,068
Adjusted EBITDA	12,847	23,373	14,846	98,807
Depreciation, depletion and amortization	7,864	7,001	22,130	22,057
Accretion on asset retirement obligation	4,810	4,314	14,430	12,941
Capital expenditures	10,818	10,369	29,315	25,904
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Adjusted EBITDA	(22,853)	(25,404)	(78,841)	(89,007)
Depreciation, depletion and amortization	324	222	838	641
Accretion on asset retirement obligation	412	327	1,236	1,056
Capital expenditures	$ 266	$ 249	$ 2,970	$ 921