Identifiable net assets (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Assets	$ 699,599	$ 701,084
Cash	173,884	178,294
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	39,202	26,053
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	48,501	48,494
Development [Member]
Segment Reporting Information [Line Items]
Assets	181,592	188,834
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	254,932	257,535
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 1,488	$ 1,874