Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Revenue	$ 62,546	$ 27,439
Operating expenses:
Research and development	83,695	65,765
General and administrative	20,985	24,995
Total operating expenses	104,680	90,760
Operating loss	(42,134)	(63,321)
Other income (expense):
Interest (expense) income, net	(167)	1,156
Other income (expense), net	507	(707)
Total other income	340	449
Loss before income tax expense and noncontrolling interest	(41,794)	(62,872)
Income tax expense	17	0
Net loss including noncontrolling interest	(41,811)	(62,872)
Net loss attributable to noncontrolling interest, net of tax	(486)	0
Net loss attributable to Arrowhead Pharmaceuticals, Inc.	$ (41,325)	$ (62,872)
Net loss per share attributable to Arrowhead Pharmaceuticals, Inc.:
Basic (in dollars per share)	$ (0.39)	$ (0.60)
Diluted (in dollars per share)	$ (0.39)	$ (0.60)
Weighted-average shares used in calculating
Basic (in shares)	106,039	104,534
Diluted (in shares)	106,039	104,534
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	$ (122)	$ (39)
Comprehensive loss	$ (41,933)	$ (62,911)