Operating results and certain other financial data for the Company’s business segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 31,220	$ 23,583	$ 23,756
Operating profit before corporate expenses	5,345	8,645	8,312
Corporate expenses	(3,071)	(3,511)	(2,556)
Operating profit	2,274	5,134	5,756
Interest expense	2,304	1,100	1,054
Depreciation, depletion and amortization	12,946	6,050	6,158
Capital expenditures	16,530	17,544	10,434
Asset Management [Member]
Segment Reporting Information [Line Items]
Revenues	2,575	2,747	2,190
Operating profit before corporate expenses	612	907	196
Corporate expenses	(843)	(909)	(646)
Depreciation, depletion and amortization	578	652	708
Capital expenditures	852	924	9,487
Mining Properties [Member]
Segment Reporting Information [Line Items]
Revenues	9,465	9,477	9,438
Operating profit before corporate expenses	8,558	8,629	8,690
Corporate expenses	(318)	(288)	(169)
Depreciation, depletion and amortization	199	218	177
Capital expenditures	522	0	0
Development [Member]
Segment Reporting Information [Line Items]
Revenues	1,563	1,152	1,164
Operating profit before corporate expenses	(2,548)	(2,576)	(2,817)
Corporate expenses	(1,557)	(2,108)	(1,581)
Depreciation, depletion and amortization	208	214	214
Capital expenditures	14,242	16,547	631
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Revenues	17,617	10,207	10,964
Operating profit before corporate expenses	(1,277)	1,685	2,243
Corporate expenses	(353)	(206)	(160)
Depreciation, depletion and amortization	11,752	4,744	4,756
Capital expenditures	914	73	316
Total Segments [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	$ 12,737	$ 5,828	$ 5,855