Identifiable net assets (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Assets	$ 674,867	$ 678,190
Investments available for sale	0	4,317
Cash	165,071	162,273
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	24,339	23,897
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	37,840	37,627
Development [Member]
Segment Reporting Information [Line Items]
Assets	176,887	176,386
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	263,586	266,429
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 7,144	$ 7,261