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Stockholders' Equity - Narrative (Details) - USD ($) |  |  |  |  |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 13, 2025 | Feb. 24, 2025 | Feb. 14, 2025 | Feb. 07, 2025 | Nov. 25, 2024 | Dec. 02, 2022 | Aug. 31, 2025 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock reserved for issuance (in shares) |  |  |  |  |  |  |  | 2,378,770 |  |
Warrant exercise price (in dollars per share) |  |  |  |  | $ 0.001 |  |  |  |  |
Number of securities called by warrants (in shares) |  |  |  |  | 917,441 |  |  |  |  |
Warrants purchase price (in dollars per share) |  |  |  |  | $ 27.25 |  |  |  |  |
Proceeds from the issuance of warrants |  |  |  |  | $ 25,000,000.0 |  |  | $ 25,000,000 | $ 0 | $ 0
Number of warrants exercised (in shares) |  |  |  |  |  |  |  | 0 |  |
Value of stock repurchased |  |  |  |  |  |  |  | $ 53,193,000 |  |
Treasury stock value |  |  |  |  |  |  |  | 53,193,000 | 0 |
Gain on settlement of treasury stock |  |  |  |  |  |  |  | $ 3,193,000 | $ 0 | $ 0
Sarepta | Sarepta Collaboration Agreement |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from sale of stock |  |  |  | $ 325,000,000 |  |  |  |  |  |
Common stock repurchased (in shares) | 2,660,989 |  |  |  |  |  | 2,660,989 |  |  |
Common stock repurchase price per share (in dollars per share) | $ 18.79 |  |  |  |  |  |  |  |  |
Value of stock repurchased | $ 50,000,000 |  |  |  |  |  | $ 50,000,000 |  |  |
Proceeds from collaboration arrangements | 50,000,000 | $ 500,000,000 | $ 500,000,000 |  |  |  | 50,000,000.0 |  |  |
Milestone payment due from collaborative agreement | 100,000,000 |  |  |  |  |  |  |  |  |
Treasury stock value | 53,200,000 |  |  |  |  |  | 53,200,000 |  |  |
Gain on settlement of treasury stock | $ 3,200,000 |  |  |  |  |  | $ 3,200,000 |  |  |
Private Placement |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Shares of common stock issued (in shares) |  |  |  |  | 11,926,301 |  |  |  |  |
Common stock offering price (in dollars per share) |  |  |  |  | $ 27.25 |  |  |  |  |
Proceeds from sale of stock |  |  |  |  | $ 325,000,000 |  |  |  |  |
ATM Agreement |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Shares issued to institutional investors (in shares) |  |  |  |  |  |  |  | 0 |  |
ATM Agreement | Maximum |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock shares value reserved for future issuance |  |  |  |  |  | $ 250,000,000 |  |  |  |
Percentage of commission to sales agent |  |  |  |  |  | 3.00% |  |  |  |
2013 and 2021 Incentive Plans and other inducement grants |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock reserved for issuance (in shares) |  |  |  |  |  |  |  | 9,851,400 | 11,492,293 |

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