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Collaboration and License Agreements - Takeda Pharmaceuticals U.S.A., Inc - Additional Information (Detail) $ in Thousands		3 Months Ended		6 Months Ended
	Oct. 07, 2020 USD ($) Obligation Bundle	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jan. 31, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		$ 151,805	$ 32,811	$ 179,244	$ 54,113
Contract liabilities, current		97,869		97,869		$ 111,055
Deferred revenue, net of current portion		89,754		89,754		$ 131,495
Takeda License Agreement \| License and Co-Funding Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 07, 2020
Ratio of Profit Sharing Structure for United States Commercialization	50/50 profit sharing
Cash received as due under collaboration agreement							$ 300,000
Number of distinct bundle \| Bundle	1
Number of distinct performance obligations \| Obligation	1
Initial transaction price	$ 300,000
Revenues		20,800	$ 25,400	41,600	$ 33,600
Contract assets		0		0
Takeda License Agreement \| License and Co-Funding Agreement \| Deferred Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, current		77,900		77,900
Deferred revenue, net of current portion		89,800		89,800
Takeda License Agreement \| License and Co-Funding Agreement \| Accrued Expenses
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, current		$ 5,000		$ 5,000
Takeda License Agreement \| Minimum [Member] \| License and Co-Funding Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of eligible to receive tiered royalties on net sales	20.00%
Takeda License Agreement \| Maximum \| License and Co-Funding Agreement
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							$ 740,000