Merger with Arch - Narrative (Details) $ in Thousands, shares in Millions			3 Months Ended
	Jan. 14, 2025 USD ($) mine state terminal shares	Jan. 13, 2025 USD ($)	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)
Business Combination [Line Items]
Number of states operating with mining and terminal facilities | state	6
Number of export terminals with ownership interest | terminal	2
Amortization expenses			$ 2,000	$ 4,000
Expected amortization rate in 2026			12.00%
Expected amortization rate in 2027			16.00%
Expected amortization rate in 2028			2.00%
Expected amortization rate in 2029			2.00%
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 | mine	11
Gross contractual amount of receivables	$ 168,299
Property, plant and equipment	1,400,000
Liability for below market lease acquired	$ 37,000
Amortized over a weighted average remaining contract term	1 year 7 months 6 days
Arch Resources, Inc | Above Market Leases
Business Combination [Line Items]
Intangible assets acquired	$ 84,000
Arch Resources, Inc | Nonrecurring Adjustments
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				51,741
Arch Resources, Inc | Nonrecurring Adjustment, Merger-Related Costs
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				49,182
Arch Resources, Inc | Nonrecurring Adjustment, Inventory Fair Value Adjustment
Business Combination [Line Items]
Pro forma expense adjustments (before tax)				$ 2,559
Arch Resources, Inc | Minimum
Business Combination [Line Items]
Identified intangible assets amortized, contract term	1 year
Arch Resources, Inc | Maximum
Business Combination [Line Items]
Identified intangible assets amortized, contract term	5 years