Identifiable net assets (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Assets	$ 699,896	$ 701,084
Cash	167,360	178,294
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	39,093	26,053
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	48,324	48,494
Development [Member]
Segment Reporting Information [Line Items]
Assets	190,350	188,834
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	253,176	257,535
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 1,593	$ 1,874