Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 1,145,087	$ 1,002,543	$ 3,370,379	$ 3,122,310
Coal
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	1,131,476	993,781	3,328,502	3,096,402
Power Generation
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	458,715	483,303	1,307,226	1,393,643
Industrial
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	252,688	210,733	896,888	686,343
Metallurgical
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	420,073	299,745	1,124,388	1,016,416
Third-Party Terminal Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	9,200	5,591	27,644	15,087
Other Revenue
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	4,411	3,171	14,233	10,821
Domestic \| Coal
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	425,402	478,430	1,257,824	1,368,601
Domestic \| Power Generation
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	353,963	398,529	1,056,398	1,154,972
Domestic \| Industrial
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	29,368	32,324	81,083	98,494
Domestic \| Metallurgical
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	42,071	47,577	120,343	115,135
Export \| Coal
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	706,074	515,351	2,070,678	1,727,801
Export \| Power Generation
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	104,752	84,774	250,828	238,671
Export \| Industrial
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	223,320	178,409	815,805	587,849
Export \| Metallurgical
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers	$ 378,002	$ 252,168	$ 1,004,045	$ 901,281