Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
REVENUE	$ 168,795,577	$ 16,142,321	$ 31,407,709
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember
OPERATING EXPENSES
Research and development	$ 81,048,686	$ 52,968,505	$ 50,904,466
General and administrative expenses	26,556,257	19,110,051	17,499,152
TOTAL OPERATING EXPENSES	107,604,943	72,078,556	68,403,618
OPERATING INCOME (LOSS)	61,190,634	(55,936,235)	(36,995,909)
OTHER INCOME (EXPENSE)
Interest income (expense), net	6,957,768	1,048,523	415,128
Change in value of derivatives		432,141	890,362
Other income (expense)		7,493	1,312,524
TOTAL OTHER INCOME (EXPENSE)	6,957,768	1,488,157	2,618,014
INCOME (LOSS) BEFORE INCOME TAXES	68,148,402	(54,448,078)	(34,377,895)
Provision for income taxes	(173,553)	(2,400)	(2,400)
NET INCOME (LOSS)	$ 67,974,849	$ (54,450,478)	$ (34,380,295)
NET INCOME (LOSS) PER SHARE - BASIC	$ 0.72	$ (0.65)	$ (0.47)
NET INCOME (LOSS) PER SHARE - DILUTED	$ 0.69	$ (0.65)	$ (0.47)
Weighted average shares outstanding - basic	93,858,857	83,638,469	73,898,598
Weighted average shares outstanding - diluted	98,607,815	83,638,469	73,898,598
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Foreign Currency Translation Adjustments	$ (370,060)	$ (54,796)	$ 25,783
COMPREHENSIVE INCOME (LOSS)	$ 67,604,789	$ (54,505,274)	$ (34,354,512)