Segment Information - Schedule of operating segment results (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($) item	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of distinct lines of business | item	2
Revenues	$ 869,931	$ 867,936
Adjusted EBITDA	277,341	320,983
Depreciation, depletion and amortization	35,479	32,210
Accretion on asset retirement obligation	5,292	4,430
Total assets	2,432,659	2,150,885	$ 2,433,108
Capital expenditures	30,541	22,288
Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	536,172	472,171
Adjusted EBITDA	263,057	259,003
Depreciation, depletion and amortization	27,853	26,952
Accretion on asset retirement obligation	615	553
Total assets	1,077,846	1,001,734
Capital expenditures	24,761	17,580
Operating Segments | Thermal
Segment Reporting Information [Line Items]
Revenues	333,759	395,765
Adjusted EBITDA	46,255	100,500
Depreciation, depletion and amortization	7,408	5,032
Accretion on asset retirement obligation	4,314	3,444
Total assets	395,624	227,009
Capital expenditures	5,493	4,002
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0
Adjusted EBITDA	(31,971)	(38,520)
Depreciation, depletion and amortization	218	226
Accretion on asset retirement obligation	363	433
Total assets	959,189	922,142
Capital expenditures	$ 287	$ 706