Collaboration and License Agreements - Amgen, Inc - Additional Information (Detail)		1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 28, 2016 USD ($) Agreement	Dec. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jul. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock		$ 250,500,000			$ 250,478,974	$ 60,521,729
Revenues			$ 27,375,778	$ 42,696,636	$ 80,359,211	$ 125,502,807
Type of Revenue [Extensible List]			arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember
Contract liabilities			$ 26,274,362		$ 26,274,362			$ 77,769,629
Amgen | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment							$ 20,000,000
Collaboration and License agreements | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Sep. 28, 2016
Number of agreements | Agreement	2
Cash received as due under collaboration agreement	$ 35,000,000
AMG-890 (ARO-LPA) Agreement | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment	10,000,000
AMG-890 (ARO-LPA) Agreement | Amgen | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development regulatory and sales milestones payments			420,000,000		420,000,000
License Collaboration and Stock Purchase Agreement | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock	$ 21,500,000
AMG 890 (ARO-LPA) and ARO-AMG1 Agreement | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues			$ 20,000,000.0	$ 0	$ 20,000,000.0	$ 300,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Contract liabilities			$ 0		$ 0
Contract assets			$ 20,000,000.0		$ 20,000,000.0
AMG 890 (ARO-LPA) and ARO-AMG1 Agreement | Amgen | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment							$ 20,000,000