Document And Entity Information (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Sep. 30, 2011
Dec. 15, 2011
Mar. 31, 2011
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2011    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2011    
Entity Registrant Name ARROWHEAD RESEARCH CORP    
Entity Central Index Key 0000879407    
Current Fiscal Year End Date --09-30    
Entity Filer Category Smaller Reporting Company    
Entity Common Stock, Shares Outstanding   10,525,941  
Entity Well-known Seasoned Issuer No    
Entity Public Float     $ 53
Entity Current Reporting Status Yes    
Entity Voluntary Filers No