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Fair Value Measurements (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Reconciliation of changes in fair value measurement, assets [abstract]    
Balance at beginning of year $ 1,075,133  
Realized gains (losses) on sales and redemptions for physical bullion (45) $ (4,537)
Change in unrealized gains (losses) 733,186 136,938
Balance at end of year 2,405,478 1,075,133
Physical bullion cost 2,127,794 1,530,636
Recurring fair value measurement    
Reconciliation of changes in fair value measurement, assets [abstract]    
Balance at beginning of year 1,075,133 871,613
Purchases 597,364 77,969
Sales   (25)
Redemptions for physical bullion (160) (6,825)
Realized gains (losses) on sales and redemptions for physical bullion (45) (4,537)
Change in unrealized gains (losses) 733,186 136,938
Balance at end of year $ 2,405,478 $ 1,075,133