Identifiable net assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 701,084	$ 678,190	$ 536,360
Investments available for sale	0	4,317	75,609
Cash	178,294	162,273	74,105
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	26,053	23,897	11,172
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	48,494	37,627	37,387
Development [Member]
Segment Reporting Information [Line Items]
Assets	188,834	176,386	196,212
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	257,535	266,429	130,472
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 1,874	$ 7,261	$ 11,403