Consolidated Statements of Operations and Comprehensive Income (Loss) (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
REVENUE	$ 21,303	$ 29,455
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember
OPERATING EXPENSES
Research and development	$ 36,555	$ 23,374
General and administrative expenses	8,802	10,934
TOTAL OPERATING EXPENSES	45,357	34,308
OPERATING INCOME (LOSS)	(24,054)	(4,853)
OTHER INCOME (EXPENSE)
Interest income (expense), net	2,169	2,180
Other income (expense)	1,153
TOTAL OTHER INCOME (EXPENSE)	3,322	2,180
INCOME (LOSS) BEFORE INCOME TAXES	(20,732)	(2,673)
NET INCOME (LOSS)	$ (20,732)	$ (2,673)
NET INCOME (LOSS) PER SHARE - BASIC	$ (0.20)	$ (0.03)
NET INCOME (LOSS) PER SHARE - DILUTED	$ (0.20)	$ (0.03)
Weighted average shares outstanding - basic	102,757	97,090
Weighted average shares outstanding - diluted	102,757	97,090
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Foreign currency translation adjustments	$ 180	$ 196
COMPREHENSIVE INCOME (LOSS)	$ (20,552)	$ (2,477)