Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2022	May 05, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Trading Symbol	ARWR
Entity Registrant Name	ARROWHEAD PHARMACEUTICALS, INC.
Entity Central Index Key	0000879407
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		105,736,200
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	001-38042
Entity Tax Identification Number	46-0408024
Entity Address, Address Line One	177 E. Colorado Blvd
Entity Address, Address Line Two	Suite 700
Entity Address, City or Town	Pasadena
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91105
City Area Code	626
Local Phone Number	304-3400
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes