Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Statement [Abstract]
Revenue	$ 15,825	$ 32,412	$ 224,638	$ 211,656
Operating expenses:
Research and development	94,757	72,180	253,333	213,930
General and administrative	23,771	33,141	67,977	92,403
Total operating expenses	118,528	105,321	321,310	306,333
Operating loss	(102,703)	(72,909)	(96,672)	(94,677)
Other income (expense):
Interest income	4,172	1,240	11,414	3,450
Interest expense	(5,158)	0	(13,064)	0
Other, net	306	(377)	821	675
Total other (loss) income	(680)	863	(829)	4,125
Loss before income tax expense and noncontrolling interest	(103,383)	(72,046)	(97,501)	(90,552)
Income tax expense	742	0	759	0
Net loss including noncontrolling interest	(104,125)	(72,046)	(98,260)	(90,552)
Net loss attributable to noncontrolling interest, net of tax	(1,179)	0	(2,664)	0
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$ (102,946)	$ (72,046)	$ (95,596)	$ (90,552)
Net loss per share attributable to Arrowhead Pharmaceuticals, Inc.:
Basic (in dollars per share)	$ (0.96)	$ (0.68)	$ (0.90)	$ (0.86)
Diluted (in dollars per share)	$ (0.96)	$ (0.68)	$ (0.90)	$ (0.86)
Weighted-average shares used in calculating
Basic (in shares)	107,004	105,753	106,597	105,273
Diluted (in shares)	107,004	105,753	106,597	105,273
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	$ (79)	$ (33)	$ (275)	$ (71)
Comprehensive loss	$ (104,204)	$ (72,079)	$ (98,535)	$ (90,623)