Segment Information - Schedule of operating segment results (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) item	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of distinct lines of business | item	2
Revenues	$ 3,145,843	$ 3,724,593	$ 2,208,042
Adjusted EBITDA	714,042	1,260,432	533,430
Depreciation, depletion and amortization	146,418	133,300	120,327
Accretion on asset retirement obligation	21,170	17,721	21,748
Total assets	2,484,173	2,433,108	2,117,160
Capital expenditures	176,037	172,728	245,440
Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	1,892,326	2,157,710	1,149,133
Adjusted EBITDA	717,834	1,021,932	442,830
Depreciation, depletion and amortization	116,550	111,772	99,171
Accretion on asset retirement obligation	2,507	2,213	2,030
Total assets	1,064,510	1,058,217	964,761
Capital expenditures	141,210	140,031	227,802
Operating Segments | Thermal
Segment Reporting Information [Line Items]
Revenues	1,253,517	1,566,883	1,057,480
Adjusted EBITDA	125,469	353,884	175,709
Depreciation, depletion and amortization	28,996	20,650	20,231
Accretion on asset retirement obligation	17,255	13,775	17,675
Total assets	437,776	381,099	205,147
Capital expenditures	33,212	28,578	5,949
Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0	1,429
Adjusted EBITDA	(129,261)	(115,384)	(85,109)
Depreciation, depletion and amortization	872	878	925
Accretion on asset retirement obligation	1,408	1,733	2,043
Total assets	981,887	993,792	947,252
Capital expenditures	$ 1,615	$ 4,119	$ 11,689