v3.26.1
Net (Loss) Income Per Share - Schedule of Computation of Basic and Diluted Net (Loss) Income Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Numerator:        
Net (loss) income attributable to Arrowhead Pharmaceuticals, Inc. $ (194,280) $ (175,241) $ (296,205) $ 22,119
Denominator:        
Weighted-average basic shares outstanding (in shares) 143,378 139,039 141,331 132,385
Effect of dilutive securities (in shares) 0 0 0 967
Weighted-average diluted shares outstanding (in shares) 143,378 139,039 141,331 133,352
Basic net (loss) income per share (in dollars per share) $ (1.36) $ (1.26) $ (2.10) $ 0.17
Diluted net (loss) income per share (in dollars per share) $ (1.36) $ (1.26) $ (2.10) $ 0.17