Consolidated Statements of Operations and Comprehensive Income (Loss) (unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
REVENUE	$ 48,148,275	$ 650,125	$ 82,806,171	$ 4,159,946
Type of Revenue [Extensible List]	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember	arwr:TechnologyLicensesCollaborativeResearchAndDevelopmentArrangementsResearchGrantsAndProductSalesMember
OPERATING EXPENSES
Research and development	$ 20,798,628	$ 12,002,354	$ 38,370,671	$ 24,921,972
General and administrative expenses	5,338,955	3,681,830	11,478,664	8,085,381
TOTAL OPERATING EXPENSES	26,137,583	15,684,184	49,849,335	33,007,353
OPERATING INCOME (LOSS)	22,010,692	(15,034,059)	32,956,836	(28,847,407)
OTHER INCOME (EXPENSE)
Interest income (expense), net	1,886,290	168,346	2,977,399	332,077
Change in value of derivatives		(18,598)		432,141
TOTAL OTHER INCOME (EXPENSE)	1,886,290	149,748	2,977,399	764,218
INCOME (LOSS) BEFORE INCOME TAXES	23,896,982	(14,884,311)	35,934,235	(28,083,189)
Provision for income taxes	0	0	0	0
NET INCOME (LOSS)	$ 23,896,982	$ (14,884,311)	$ 35,934,235	$ (28,083,189)
NET INCOME (LOSS) PER SHARE - BASIC	$ 0.25	$ (0.18)	$ 0.39	$ (0.35)
NET INCOME (LOSS) PER SHARE - DILUTED	$ 0.24	$ (0.18)	$ 0.37	$ (0.35)
Weighted average shares outstanding - basic	94,155,407	84,083,937	92,623,615	79,406,838
Weighted average shares outstanding - diluted	98,082,644	84,083,937	97,214,546	79,406,838
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Foreign Currency Translation Adjustments	$ (28,162)	$ 1,561	$ (50,342)	$ (7,967)
COMPREHENSIVE INCOME (LOSS)	$ 23,868,820	$ (14,882,750)	$ 35,883,893	$ (28,091,156)