Business segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 10,133	$ 10,114
Operating profit before corporate expenses	4,924	4,647
General and administrative expenses	(2,042)	(1,793)
Operating profit	2,882	2,854
Interest expense	911	1,006
Depreciation, depletion and amortization	2,596	2,842
Capital expenditures	6,205	1,206
Industrial Commercial [Member]
Segment Reporting Information [Line Items]
Revenues	1,453	1,070
Operating profit before corporate expenses	812	591
General and administrative expenses	(250)	(296)
Depreciation, depletion and amortization	363	278
Capital expenditures	145	480
Mining Properties [Member]
Segment Reporting Information [Line Items]
Revenues	2,963	3,282
Operating profit before corporate expenses	2,724	3,013
General and administrative expenses	(278)	(223)
Depreciation, depletion and amortization	149	183
Capital expenditures	20	0
Development [Member]
Segment Reporting Information [Line Items]
Revenues	303	486
Operating profit before corporate expenses	(60)	50
General and administrative expenses	(1,278)	(1,085)
Depreciation, depletion and amortization	42	55
Capital expenditures	5,954	594
Multifamily Segment [Member]
Segment Reporting Information [Line Items]
Revenues	5,414	5,276
Operating profit before corporate expenses	1,448	993
General and administrative expenses	(236)	(189)
Depreciation, depletion and amortization	1,981	2,264
Capital expenditures	86	132
Total Segments [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	$ 2,535	$ 2,780