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Related Party Transactions - Additional Information (Detail) (USD $) | 1 Months Ended | 12 Months Ended | 3 Months Ended
--- | --- | --- | ---
Aug. 31, 2010 | Sep. 30, 2012 | Sep. 30, 2011 | Dec. 31, 2012 Nanotope, Inc. [Member]
Related Party Transaction [Line Items] |  |  |  |
Shares owned by Arrowhead's President and CEO |  |  |  | 1,395,900
Percentage of outstanding voting securities owned by Arrowhead's President and CEO |  |  |  | 14.20%
Monthly remuneration of employee | $ 10,000 |  |  |
Remuneration of Mr. Vincent Anzalone |  | $ 120,000 | $ 120,000 |

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- Details
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