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Investment in Gold - Investment in Gold (Parenthetical) (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
oz
Sep. 30, 2013
oz
Investment in Gold [Line Items]    
Gold receivable, Ounces of gold 0 0
Gold payable, Ounces of gold 192,900 115,900
Gold receivable $ 0 $ 0
Gold payable $ 231,752 $ 153,680