Unconsolidated Subsidiaries (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Variable interest entity, reporting entity involvement, maximum risk of loss	$ 5,500	$ 5,000
Other non-current assets
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated subsidiaries	$ 14,100	12,400
Unconsolidated Subsidiaries
Schedule of Equity Method Investments [Line Items]
Ownership (percent)	100.00%
Investments in unconsolidated subsidiaries	$ 14,137	12,371
Unconsolidated Mines \| NACoal
Schedule of Equity Method Investments [Line Items]
Dividends from unconsolidated mines	$ 48,800	$ 45,800

Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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