Segment Information - Schedule of operating segment results (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) item	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of distinct lines of business | item			2
Revenues	$ 744,601	$ 863,835	$ 2,371,826	$ 2,865,129
Adjusted EBITDA	126,291	222,956	534,018	1,003,906
Depreciation, depletion and amortization	36,717	33,958	108,273	98,948
Accretion on asset retirement obligation	5,292	4,430	15,877	13,290
Total assets	2,365,858	2,319,862	2,365,858	2,319,862	$ 2,433,108
Capital expenditures	44,424	41,360	121,030	94,517
Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	432,835	444,306	1,420,758	1,640,970
Adjusted EBITDA	128,322	155,185	524,218	810,615
Depreciation, depletion and amortization	29,494	28,354	85,575	82,738
Accretion on asset retirement obligation	651	553	1,880	1,660
Total assets	1,046,404	1,020,849	1,046,404	1,020,849
Capital expenditures	33,806	36,389	94,205	79,896
Operating Segments | Thermal
Segment Reporting Information [Line Items]
Revenues	311,766	419,529	951,068	1,224,159
Adjusted EBITDA	23,373	96,812	98,807	290,648
Depreciation, depletion and amortization	7,001	5,388	22,057	15,554
Accretion on asset retirement obligation	4,314	3,444	12,941	10,331
Total assets	415,373	325,580	415,373	325,580
Capital expenditures	10,369	4,604	25,904	13,200
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Adjusted EBITDA	(25,404)	(29,041)	(89,007)	(97,357)
Depreciation, depletion and amortization	222	216	641	656
Accretion on asset retirement obligation	327	433	1,056	1,299
Total assets	904,081	973,433	904,081	973,433
Capital expenditures	$ 249	$ 367	$ 921	$ 1,421