Identifiable net assets (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Assets	$ 676,990	$ 678,190
Investments available for sale at fair value	0	4,317
Cash	145,365	162,273
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	24,468	23,897
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	48,715	37,627
Development [Member]
Segment Reporting Information [Line Items]
Assets	190,883	176,386
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	259,369	266,429
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 8,190	$ 7,261