Collaboration and License Agreements - Takeda Pharmaceutical Company Limited (Details) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Oct. 07, 2020 USD ($) obligation bundle	Mar. 31, 2023 USD ($) $ / shares	Mar. 31, 2022 USD ($) $ / shares	Mar. 31, 2023 USD ($) $ / shares	Mar. 31, 2022 USD ($) $ / shares	Sep. 30, 2022 USD ($)	Jan. 31, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development regulatory and sales milestones payments		$ 3,600,000		$ 3,600,000
Revenues		$ 146,267	$ 151,805	$ 208,813	$ 179,244
Diluted (in dollars per share) | $ / shares		$ 0.45	$ 0.41	$ 0.07	$ (0.18)
Deferred revenue, net of current portion		$ 1,075		$ 1,075		$ 55,950
Deferred revenue		29,839		29,839		$ 74,099
Takeda | License and Co-Funding Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash received as due under collaboration agreement							$ 300,000
Milestone payment		40,000		40,000
Number of distinct performance obligations | obligation	1
Number of distinct bundle | bundle	1
Initial transaction price	$ 300,000
Revenues		$ 61,400		$ 61,400
Diluted (in dollars per share) | $ / shares		$ 0.57		$ 0.57
Milestone payment receivable		$ 40,000		$ 40,000
Takeda | License and Co-Funding Agreement | Deferred Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, net of current portion		30,900		30,900
Deferred revenue		29,800		29,800
Takeda | License and Co-Funding Agreement | Accrued Expenses
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		9,400		9,400
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		$ 527,500