Collaboration and License Agreements - Takeda Pharmaceutical Company Limited (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 07, 2020 USD ($) bundle obligation	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2022 USD ($) $ / shares	Sep. 30, 2021 USD ($) $ / shares	Mar. 31, 2023 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development regulatory and sales milestones payments		$ 2,800,000
Revenues		$ 240,735	$ 243,231	$ 138,287
Diluted (in dollars per share) | $ / shares		$ (1.92)	$ (1.67)	$ (1.36)
Deferred revenue		$ 866	$ 74,099
Accrued expenses		39,763	$ 46,856
Takeda | License and Co-Funding Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct performance obligations | obligation	1
Number of distinct bundle | bundle	1
Initial transaction price	$ 300,000
Milestone payment					$ 40,000
Revenues		$ 70,500
Diluted (in dollars per share) | $ / shares		$ 0.66
Deferred revenue		$ 900
Accrued expenses		4,500
Takeda | License and Co-Funding Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of eligible to receive tiered royalties on net sales	20.00%
Takeda | License and Co-Funding Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of eligible to receive tiered royalties on net sales	25.00%
Development regulatory and sales milestones payments		$ 527,500