Consolidated Statements of Operations and Comprehensive Income (Loss) (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
REVENUE	$ 32,811	$ 23,529	$ 54,113	$ 52,983
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantAndProductSalesMember
OPERATING EXPENSES
Research and development	$ 44,697	$ 29,443	$ 81,251	$ 52,817
General and administrative expenses	16,346	16,326	25,147	27,260
TOTAL OPERATING EXPENSES	61,043	45,769	106,398	80,077
OPERATING INCOME (LOSS)	(28,232)	(22,240)	(52,285)	(27,094)
OTHER INCOME (EXPENSE)
Interest income, net	1,524	2,404	3,692	4,585
Other income (expense)	(110)		1,043
TOTAL OTHER INCOME (EXPENSE)	1,414	2,404	4,735	4,585
INCOME (LOSS) BEFORE INCOME TAXES	(26,818)	(19,836)	(47,550)	(22,509)
NET INCOME (LOSS)	$ (26,818)	$ (19,836)	$ (47,550)	$ (22,509)
NET INCOME (LOSS) PER SHARE - BASIC	$ (0.26)	$ (0.20)	$ (0.46)	$ (0.23)
NET INCOME (LOSS) PER SHARE - DILUTED	$ (0.26)	$ (0.20)	$ (0.46)	$ (0.23)
Weighted average shares outstanding - basic	103,867	101,653	103,303	99,359
Weighted average shares outstanding - diluted	103,867	101,653	103,303	99,359
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Foreign currency translation adjustments	$ (96)	$ (433)	$ 84	$ (238)
COMPREHENSIVE INCOME (LOSS)	$ (26,914)	$ (20,269)	$ (47,466)	$ (22,747)