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Investment in Gold - Investment in Gold (Parenthetical) (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
oz
Sep. 30, 2011
oz
Sep. 30, 2010
oz
Investment in Gold (Textual) [Abstract]      
Gold receivable ounces of gold 0.0 0.0 195.4
Gold payable ounces of gold 339.3 321.2 58.6
Gold receivable $ 0 $ 0 $ 255,409
Gold payable $ 602,591 $ 520,297 $ 76,622