Note 7 - Mineral Rights, Net - Composition of Mineral Rights (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Mineral Properties, carrying value	$ 687,959	$ 687,959
Mineral Properties, accumulated depletion	(327,099)	(320,972)
Mineral Properties, net book value	360,860	366,987
Coal Properties [Member]
Mineral Properties, carrying value	653,808	653,808
Mineral Properties, accumulated depletion	(310,427)	(304,412)
Mineral Properties, net book value	343,381	349,396
Aggregates Properties [Member]
Mineral Properties, carrying value	8,655	8,655
Mineral Properties, accumulated depletion	(4,439)	(4,364)
Mineral Properties, net book value	4,216	4,291
Oil and Gas Royalty Properties [Member]
Mineral Properties, carrying value	12,354	12,354
Mineral Properties, accumulated depletion	(10,621)	(10,584)
Mineral Properties, net book value	1,733	1,770
Other [Member]
Mineral Properties, carrying value	13,142	13,142
Mineral Properties, accumulated depletion	(1,612)	(1,612)
Mineral Properties, net book value	$ 11,530	$ 11,530

The accumulated decrease in the carrying value of the mineral properties as a result of mine or mineral production.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

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- Definition

Carrying amount at the balance sheet date of mineral properties, gross of adjustments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

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- Definition

Mineral properties, net of adjustments.

+ References

+ Details

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