v3.19.1
Document and Entity Information - shares
6 Months Ended
Mar. 31, 2019
May 06, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Trading Symbol ARWR  
Entity Registrant Name ARROWHEAD PHARMACEUTICALS, INC.  
Entity Central Index Key 0000879407  
Current Fiscal Year End Date --09-30  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   94,814,086
Entity Small Business false  
Entity Emerging Growth Company false