Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance	395,950
Options granted and outstanding to purchase	3,423,490		3,419,285	1,910,794	729,096
Number of Options Outstanding, Granted	105,000		1,509,166	1,229,500
Options granted outside of Equity Incentive plans	105,000
Stock-based compensation expense	$ 521,138	$ 395,674
Fair value of the options granted	531,510	6,083
Intrinsic value of the options exercised	314,858	554
Dividend yield	0.00%
Calando Pharmaceuticals Inc
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of the options granted	0	0
Pre-tax compensation expense	28,695
Weighted average period to recognize pre-tax compensation expense	1 year 9 months 18 days
Arrowhead
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Pre-tax compensation expense	$ 5,111,999
Weighted average period to recognize pre-tax compensation expense	3 years
2000 Stock Option Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance	153,200
Options granted and outstanding to purchase	152,900
2004 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance	2,902,360
Options granted and outstanding to purchase	2,874,640
Number of Options Outstanding, Granted	0