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