Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
REVENUE	$ 87,992,066	$ 168,795,577	$ 16,142,321
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember
OPERATING EXPENSES
Research and development	$ 128,874,979	$ 81,048,686	$ 52,968,505
General and administrative expenses	52,275,890	26,556,257	19,110,051
TOTAL OPERATING EXPENSES	181,150,869	107,604,943	72,078,556
OPERATING INCOME (LOSS)	(93,158,803)	61,190,634	(55,936,235)
OTHER INCOME (EXPENSE)
Interest income (expense), net	9,190,501	6,957,768	1,048,523
Change in value of derivatives			432,141
Other Income (expense)	(582,524)		7,493
TOTAL OTHER INCOME (EXPENSE)	8,607,977	6,957,768	1,488,157
INCOME (LOSS) BEFORE INCOME TAXES	(84,550,826)	68,148,402	(54,448,078)
Provision for income taxes	(2,400)	(173,553)	(2,400)
NET INCOME (LOSS)	$ (84,553,226)	$ 67,974,849	$ (54,450,478)
NET INCOME (LOSS) PER SHARE - BASIC	$ (0.84)	$ 0.72	$ (0.65)
NET INCOME (LOSS) PER SHARE - DILUTED	$ (0.84)	$ 0.69	$ (0.65)
Weighted average shares outstanding - basic	100,722,224	93,858,857	83,638,469
Weighted average shares outstanding - diluted	100,722,224	98,607,815	83,638,469
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Foreign currency translation adjustments	$ 410,057	$ (370,060)	$ (54,796)
COMPREHENSIVE INCOME (LOSS)	$ (84,143,169)	$ 67,604,789	$ (54,505,274)