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Significant Accounting Policies - Summary of Trust's Investments at Fair Value (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Sep. 30, 2017
Investment Holdings [Line Items]    
Investment in Gold $ 36,013,428 $ 35,669,225
Level 1 [Member]    
Investment Holdings [Line Items]    
Investment in Gold 36,013,428 35,669,225
Level 1 [Member] | Investment in Gold [Member]    
Investment Holdings [Line Items]    
Investment in Gold 36,013,428 35,669,225
Level 2 [Member]    
Investment Holdings [Line Items]    
Investment in Gold 0 0
Level 2 [Member] | Investment in Gold [Member]    
Investment Holdings [Line Items]    
Investment in Gold 0 0
Level 3 [Member]    
Investment Holdings [Line Items]    
Investment in Gold 0 0
Level 3 [Member] | Investment in Gold [Member]    
Investment Holdings [Line Items]    
Investment in Gold $ 0 $ 0