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Note 9 - Mineral Rights, Net - Composition of Mineral Rights (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Mineral Properties, carrying value $ 695,113 $ 695,408
Mineral Properties, accumulated depletion (315,475) (300,925)
Mineral Properties, net book value 379,638 394,483
Coal Properties [Member]    
Mineral Properties, carrying value 660,961 661,256
Mineral Properties, accumulated depletion (299,404) (285,470)
Mineral Properties, net book value 361,557 375,786
Aggregates Properties [Member]    
Mineral Properties, carrying value 8,655 8,655
Mineral Properties, accumulated depletion (4,065) (3,761)
Mineral Properties, net book value 4,590 4,894
Oil and Gas Royalty Properties [Member]    
Mineral Properties, carrying value 12,354 12,354
Mineral Properties, accumulated depletion (10,394) (10,082)
Mineral Properties, net book value 1,960 2,272
Other [Member]    
Mineral Properties, carrying value 13,143 13,143
Mineral Properties, accumulated depletion (1,612) (1,612)
Mineral Properties, net book value $ 11,531 $ 11,531