Consolidated Statements of Operations and Comprehensive Income (Loss) (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
REVENUE	$ 45,891	$ 27,376	$ 100,004	$ 80,359
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember
OPERATING EXPENSES
Research and development	$ 59,325	$ 32,573	$ 140,576	$ 85,390
General and administrative expenses	18,434	10,749	43,581	38,009
TOTAL OPERATING EXPENSES	77,759	43,322	184,157	123,399
OPERATING INCOME (LOSS)	(31,868)	(15,946)	(84,153)	(43,040)
OTHER INCOME (EXPENSE)
Interest income, net	1,280	2,335	4,972	6,920
Other income (expense)	664		1,707
TOTAL OTHER INCOME (EXPENSE)	1,944	2,335	6,679	6,920
INCOME (LOSS) BEFORE INCOME TAXES	(29,924)	(13,611)	(77,474)	(36,120)
NET INCOME (LOSS)	$ (29,924)	$ (13,611)	$ (77,474)	$ (36,120)
NET INCOME (LOSS) PER SHARE - BASIC	$ (0.29)	$ (0.13)	$ (0.75)	$ (0.36)
NET INCOME (LOSS) PER SHARE - DILUTED	$ (0.29)	$ (0.13)	$ (0.75)	$ (0.36)
Weighted average shares outstanding - basic	104,099	101,843	103,569	100,184
Weighted average shares outstanding - diluted	104,099	101,843	103,569	100,184
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Foreign currency translation adjustments	$ (40)	$ 454	$ 44	$ 216
COMPREHENSIVE INCOME (LOSS)	$ (29,964)	$ (13,157)	$ (77,430)	$ (35,904)