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Counterparty Risk - Additional Information (Detail)
6 Months Ended 12 Months Ended
Mar. 31, 2018
Sep. 30, 2017
Risk and uncertainty [Line Items]    
Gold Delivery Agreement termination period Jun. 28, 2019 Jun. 28, 2019
SPDR Long Dollar Gold Trust [Member]    
Risk and uncertainty [Line Items]    
Gold Delivery Agreement termination period Jun. 28, 2019 Jun. 28, 2019