Identifiable net assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets	$ 678,190	$ 536,360	$ 538,148
Investments available for sale	4,317	75,609	137,867
Cash	162,273	74,105	26,793
Asset Management [Member]
Segment Reporting Information [Line Items]
Assets	23,897	11,172	18,468
Mining Properties [Member]
Segment Reporting Information [Line Items]
Assets	37,627	37,387	38,409
Development [Member]
Segment Reporting Information [Line Items]
Assets	176,386	196,212	179,357
Stabilized Joint Venture [Member]
Segment Reporting Information [Line Items]
Assets	266,429	130,472	133,956
Unallocated Corporate Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 7,261	$ 11,403	$ 3,298