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