Summary of Significant Accounting Policies Summary of Unearned Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Contract Liabilities
Revenue Recognized	$ (8,134)	$ 0	$ (15,682)	$ 0
Franco-Nevada
Contract Liabilities
Opening Balance	10,505	12,473	11,061	12,918
Revenue Recognized	116	313	672	758
Closing Balance	10,389	12,160	10,389	12,160
Kensington
Contract Liabilities
Opening Balance	8,018	0	15,010	0
Revenue Recognized	8,018	0	15,010	0
Closing Balance	15,006	25,021	15,006	25,021
Deferred Revenue, Additions	$ 15,006	$ 25,021	$ 15,006	$ 25,021