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Significant Accounting Policies - Summary of Fund's Investments at Fair Value (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Sep. 30, 2017
Investment Holdings [Line Items]    
Fund's investments at fair value $ 16,666 $ 14,406
SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value 16,666 14,406
Investment in Gold [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value 16,666 14,406
Investment in Gold [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value 16,666 14,406
Fair Value, Inputs, Level 1 [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value 16,666 14,406
Fair Value, Inputs, Level 1 [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value 16,666 14,406
Fair Value, Inputs, Level 1 [Member] | Investment in Gold [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value 16,666 14,406
Fair Value, Inputs, Level 1 [Member] | Investment in Gold [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value $ 16,666 14,406
Fair Value, Inputs, Level 1 [Member] | Gold Delivery Agreement [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 1 [Member] | Gold Delivery Agreement [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 2 [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 2 [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 2 [Member] | Investment in Gold [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 2 [Member] | Investment in Gold [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 2 [Member] | Gold Delivery Agreement [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 2 [Member] | Gold Delivery Agreement [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 3 [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 3 [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 3 [Member] | Investment in Gold [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 3 [Member] | Investment in Gold [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 3 [Member] | Gold Delivery Agreement [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   0
Fair Value, Inputs, Level 3 [Member] | Gold Delivery Agreement [Member] | SPDR Long Dollar Gold Trust [Member]    
Investment Holdings [Line Items]    
Fund's investments at fair value   $ 0