Note 2 - Revenues from Contracts with Customers - Disaggregation of Revenue (Details) - Mineral Rights Segment [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Operating Segments [Member]
Revenue from contract with customers	$ 46,705	$ 55,145
Coal Royalty Revenues [Member]
Revenue from contract with customers	29,574	35,498
Production Lease Minimum Revenues [Member]
Revenue from contract with customers	558	2,725
Minimum Lease Straight-line Revenues [Member]
Revenue from contract with customers	4,019	4,050
Oil and Gas Royalty Revenues [Member]
Revenue from contract with customers	1,386	2,444
Carbon Neutral Revenues [Member]
Revenue from contract with customers	185	595
Property Tax Revenues [Member]
Revenue from contract with customers	1,711	1,637
Wheelage Revenues [Member]
Revenue from contract with customers	1,990	1,738
Coal Overriding Royalty Revenues [Member]
Revenue from contract with customers	1,386	880
Lease Amendment Revenues [Member]
Revenue from contract with customers	1,200	655
Aggregates Royalty Revenues [Member]
Revenue from contract with customers	1,118	853
Other Revenues [Member]
Revenue from contract with customers	170	185
Royalty and Other Mineral Rights [Member]
Revenue from contract with customers	43,297	51,260
Transportation and Processing Services [Member]
Revenue from contract with customers	$ 3,408	$ 3,885