Organization and Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended			9 Months Ended
	Jul. 27, 2025	Feb. 24, 2025	Feb. 07, 2025	Nov. 25, 2024	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Sep. 30, 2024	Sep. 30, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash, cash equivalents and restricted cash					$ 129,793		$ 69,399	$ 129,793	$ 69,399	$ 102,685	$ 110,891
Restricted cash					2,200			2,200
Available-for-sale securities					770,579			770,579		$ 578,276
Increase (decrease) in cash and investments								219,400
Proceeds from the issuance of warrants				$ 25,000				25,000	0
Repayments of credit facility								201,625	0
Interest income					11,019		$ 6,498	28,236	$ 15,550
Development regulatory and sales milestones payments					$ 13,300,000			$ 13,300,000
Sarepta | Sarepta Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from sale of stock			$ 325,000
Shares of common stock issued (in shares)			11,926,301
Common stock sold price (in dollars per share)			$ 27.25
Upfront payment		$ 500,000
Annual fees			$ 250,000
Annual installments period			5 years
Enrollment related milestone payments			$ 300,000
Future potential milestone payments			$ 10,000,000
Sarepta | Sarepta Collaboration Agreement | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone payments	$ 100,000
Future potential milestone payments	$ 200,000
GSK | GSK-HBV Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone payments						$ 2,500