Merger with Arch - Narrative (Details) $ in Thousands, shares in Millions				3 Months Ended	9 Months Ended
	Jan. 14, 2025 USD ($) state mine shares	Jan. 13, 2025 USD ($)	Jan. 01, 2024 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2025 USD ($)
Business Combination [Line Items]
Number of states operating with mining and terminal facilities | state	6
Amortized over a weighted average remaining contract term					1 year 7 months 6 days
Amortization expenses				$ 8,000	$ 23,000
Expected amortization rate in 2025				66.00%	66.00%
Expected amortization rate in 2026				16.00%	16.00%
Expected amortization rate in 2027				16.00%	16.00%
Expected amortization rate in 2028				2.00%	2.00%
Expected amortization rate in 2029				2.00%	2.00%
Minimum
Business Combination [Line Items]
Identified intangible assets amortized, contract term					1 year
Maximum
Business Combination [Line Items]
Identified intangible assets amortized, contract term					5 years
Arch Resources, Inc
Business Combination [Line Items]
Issued (in shares) | shares	24.3
Business acquisition, percentage	45.00%			35.00%	35.00%
Equity portion of purchase consideration	$ 2,481,368
Purchase price consideration		$ 98,075
Number of mines | mine	11
Gross contractual amount of receivables	$ 168,299
Property, plant and equipment					$ 1,400,000
Revenue					1,531,951
Loss before income tax			$ 135,022		274,610
Business acquisition, transaction costs			$ 92,698
Acquisition related costs					39,765
Amortization of related to inventory step-up amount					2,559
Arch Resources, Inc | Other Noncurrent Assets
Business Combination [Line Items]
Intangible assets				$ 84,000	84,000
Arch Resources, Inc | Other Noncurrent Liabilities
Business Combination [Line Items]
Intangible assets				$ 37,000	$ 37,000