Collaboration and License Agreements - Takeda Pharmaceuticals U.S.A., Inc - Additional Information (Detail) $ in Thousands		12 Months Ended
	Oct. 07, 2020 USD ($) Obligation Bundle	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jan. 31, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		$ 138,287	$ 87,992	$ 168,796
Contract liabilities, current		111,055	19,291
Deferred revenue, net of current portion		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		90,800	$ 0	$ 0
Contract assets		0
Deferred revenue, net of current portion		124,800
Takeda License Agreement | License and Co-Funding Agreement | Deferred Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, current		84,400
Takeda License Agreement | License and Co-Funding Agreement | Accrued Expenses
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, current		$ 3,100
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