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Significant Accounting Policies - Additional Information (Detail)
 3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Mar. 31, 2018
USD ($)
t
shares
Mar. 31, 2017
USD ($)
Sep. 30, 2017
USD ($)
t
Schedule Of Significant Accounting Policies [Line Items]          
Fair value of assets and liabilities, amount transferred between levels     $ 0   $ 0
Maximum number of business days within which ownership of the gold is transferred     2 days    
Minimum denomination of shares issued redeemed against gold | shares     100,000    
Net realized and change in unrealized gain/(loss) on investment in gold $ 742,014,000 $ 2,244,786,000 $ 1,096,754,000 $ (2,640,593,000)  
Net realized gain/(loss) from investment in gold sold to pay expenses 1,918,000 (898,000) 2,508,000 (830,000) 252,000
Net realized gain/(loss) from gold distributed for the redemption of shares 148,686,000 (71,852,000) 187,077,000 (277,748,000) (222,162,000)
Net change in unrealized appreciation/(depreciation) on investment in gold 591,410,000 $ 2,317,536,000 907,169,000 $ (2,362,015,000) (1,535,978,000)
Liability for uncertain tax positions - current $ 0   $ 0   $ 0
Bank of England [Member]          
Schedule Of Significant Accounting Policies [Line Items]          
Gold held by subcustodian | t     0   0