Note 2 - Revenues from Contracts with Customers - Disaggregation of Revenue (Details) - Mineral Rights Segment [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Operating Segments [Member]
Revenue from contract with customers	$ 48,495	$ 50,908	$ 147,708	$ 152,377
Coal Royalty Revenues [Member]
Revenue from contract with customers	35,142	34,193	99,509	101,234
Production Lease Minimum Revenues [Member]
Revenue from contract with customers	531	1,365	1,340	4,213
Minimum Lease Straight-line Revenues [Member]
Revenue from contract with customers	4,019	4,176	12,057	12,276
Oil and Gas Royalty Revenues [Member]
Revenue from contract with customers	1,477	1,787	5,310	6,212
Carbon Neutral Revenues [Member]
Revenue from contract with customers	245	316	524	1,201
Property Tax Revenues [Member]
Revenue from contract with customers	420	2,105	3,841	5,261
Wheelage Revenues [Member]
Revenue from contract with customers	2,055	2,225	6,004	6,506
Coal Overriding Royalty Revenues [Member]
Revenue from contract with customers	544	297	2,970	1,633
Lease Amendment Revenues [Member]
Revenue from contract with customers	1,117	1,699	3,559	3,010
Aggregates Royalty Revenues [Member]
Revenue from contract with customers	1,198	1,011	3,562	2,770
Other Revenues [Member]
Revenue from contract with customers	241	441	729	854
Royalty and Other Mineral Rights [Member]
Revenue from contract with customers	46,989	49,615	139,405	145,170
Transportation and Processing Services [Member]
Revenue from contract with customers	$ 1,506	$ 1,293	$ 8,303	$ 7,207