Note 2 - Revenues From Contracts With Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue from contract with customers	$ 50,405	$ 68,533	$ 170,570	$ 205,811
Mineral Rights Segment [Member] | Operating Segments [Member]
Revenue from contract with customers	51,653	72,497	176,739	215,349
Coal Royalty Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	37,605	55,544	124,108	161,527
Production Lease Minimum Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	437	850	1,773	2,025
Minimum Lease Straight-line Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	4,117	4,464	12,414	13,414
Carbon Neutral Initiatives [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	(39)	681	4,322	2,914
Property Tax Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	1,809	1,770	5,246	4,710
Wheelage Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	2,072	2,385	7,082	9,538
Coal Overriding Royalty Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	227	827	2,064	1,165
Lease Amendment Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	1,071	623	2,485	2,322
Aggregates Royalty Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	662	736	2,164	2,175
Oil and Gas Royalty Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	1,317	324	6,956	5,126
Other Revenues [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	1,127	329	1,956	895
Transportation and Processing Services [Member] | Mineral Rights Segment [Member]
Revenue from contract with customers	$ 1,248	$ 3,964	$ 6,169	$ 9,538