Identifiable net assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Assets	$ 701,157	$ 701,084
Cash	166,674	178,294
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	39,155	26,053
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	48,126	48,494
Development [Member]
Segment Reporting Information [Line Items]
Assets	194,297	188,834
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	251,677	257,535
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 1,228	$ 1,874