Unaudited Quarterly Financial Data - Summary of Unaudited Quarterly Financial Data (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 43,292,770	$ 42,696,636	$ 48,148,275	$ 34,657,896	$ 11,255,000	$ 727,375	$ 650,125	$ 3,509,821	$ 168,795,577	$ 16,142,321	$ 31,407,709
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember
Operating Income (Loss)	$ 9,638,049	$ 18,595,749	$ 22,010,692	$ 10,946,144	$ (11,169,109)	$ (15,919,719)	$ (15,034,059)	$ (13,813,348)	$ 61,190,634	$ (55,936,235)	$ (36,995,909)
Net Income (Loss)	$ 11,704,906	$ 20,335,708	$ 23,896,982	$ 12,037,253	$ (10,761,272)	$ (15,606,017)	$ (14,884,311)	$ (13,198,878)	$ 67,974,849	$ (54,450,478)	$ (34,380,295)
Net Income (Loss) per share - BASIC	$ 0.12	$ 0.21	$ 0.25	$ 0.13	$ (0.12)	$ (0.18)	$ (0.18)	$ (0.18)	$ 0.72	$ (0.65)	$ (0.47)
Net Income (Loss) per share - DILUTED	$ 0.12	$ 0.21	$ 0.24	$ 0.13	$ (0.12)	$ (0.18)	$ (0.18)	$ (0.18)	$ 0.69	$ (0.65)	$ (0.47)