business segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Revenues	$ 10,591	$ 9,294	$ 31,401	$ 27,629
Operating profit before corporate expenses	3,785	2,583	11,729	8,155
Corporate expenses	(889)	(734)	(3,212)	(2,876)
Operating profit	2,896	1,849	8,517	5,279
Interest expense	1,116	738	3,251	2,215
Depreciation, depletion and amortization			8,557	8,696
Capital expenditures	2,449	8,726	4,634	26,137
Asset Management [Member]
Segment Reporting Information [Line Items]
Revenues	1,442	935	3,932	2,686
Operating profit before corporate expenses	697	392	1,855	1,103
Corporate expenses	(177)	(127)	(630)	(496)
Depreciation, depletion and amortization	369	219	1,006	683
Capital expenditures	12	202	557	797
Mining Properties [Member]
Segment Reporting Information [Line Items]
Revenues	3,082	2,471	9,628	7,779
Operating profit before corporate expenses	2,608	2,083	8,391	6,764
Corporate expenses	(99)	(83)	(360)	(325)
Depreciation, depletion and amortization	138	172	472	416
Capital expenditures	0	1	0	11,218
Development [Member]
Segment Reporting Information [Line Items]
Revenues	434	412	1,387	1,203
Operating profit before corporate expenses	(444)	(865)	(1,377)	(2,164)
Corporate expenses	(529)	(457)	(1,918)	(1,794)
Depreciation, depletion and amortization	44	47	140	139
Capital expenditures	2,179	8,548	3,640	13,927
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Revenues	5,633	5,476	16,454	15,961
Operating profit before corporate expenses	924	973	2,860	2,452
Corporate expenses	(84)	(67)	(304)	(261)
Depreciation, depletion and amortization	2,265	2,306	6,797	7,272
Capital expenditures	258	(25)	437	195
Total Segments [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	$ 2,816	$ 2,744	$ 8,415	$ 8,510