Merger with Arch - Narrative (Details) $ in Thousands, shares in Millions			12 Months Ended
	Jan. 14, 2025 USD ($) mine terminal state shares	Jan. 13, 2025 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Business Combination [Line Items]
Number of states having mining operations and terminal facilities | state	6
Number of export terminals with ownership interest | terminal	2
Acquired intangible assets weighted-average contractual term			1 year 7 months 6 days
Amortization expense			$ 32,000
Expected amortization rate in 2026			16.00%
Expected amortization rate in 2027			16.00%
Expected amortization rate in 2028			2.00%
Expected amortization rate in 2029			2.00%
Minimum
Business Combination [Line Items]
Acquired intangible assets contractual term			1 year
Maximum
Business Combination [Line Items]
Acquired intangible assets contractual term			5 years
Arch Resources, Inc
Business Combination [Line Items]
Stock issued (in shares) | shares	24.3
Business acquisition, percentage	45.00%
Equity portion of purchase consideration	$ 2,481,368
Purchase price consideration		$ 98,075
Number of mines owned | mine	11
Gross contractual amount of receivables acquired	$ 168,299
Property, plant and equipment fair value adjustments			$ 1,400,000
Revenue attributable to acquiree			2,048,154
Loss before income tax attributable to acquiree			431,393
Arch Resources, Inc | Nonrecurring Adjustments
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				$ 161,102
Arch Resources, Inc | Nonrecurring Adjustment, Transaction and Employee Related Costs
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				92,698
Arch Resources, Inc | Nonrecurring Adjustment, Merger-Related Costs
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				65,845
Arch Resources, Inc | Nonrecurring Adjustment, Inventory Fair Value Adjustment
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				$ 2,559
Arch Resources, Inc | Other Noncurrent Assets
Business Combination [Line Items]
Intangible assets acquired			84,000
Arch Resources, Inc | Other Noncurrent Liabilities
Business Combination [Line Items]
Intangible assets acquired			$ 37,000