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Collaboration and License Agreements - Janssen Pharmaceuticals, Inc - Additional Information (Detail)		3 Months Ended		9 Months Ended
	Oct. 03, 2018 USD ($) obligation	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	May 31, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		$ 32,412,000	$ 45,891,000	$ 211,656,000	$ 100,004,000
Deferred revenue		84,288,000		84,288,000		$ 111,055,000
Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 252,700,000
JJDC \| Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock	75,000,000
Janssen \| Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash received as due under collaboration agreement	175,000,000
Janssen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment	73,000,000
Development, regulatory and sales milestones payments		4,900,000,000		4,900,000,000
Janssen \| License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments	1,600,000,000
Janssen \| Collaboration Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments	600,000,000
Janssen \| JNJ-3989 (ARO-HBV) Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment	$ 25,000,000
Number of distinct performance obligations \| obligation	1
Revenues		0	0	0	20,200,000
Contract assets		0		0
Deferred revenue		0		0
Janssen \| JNJ-75220795 (ARO-JNJ1)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment			10,000,000		10,000,000		$ 10,000,000
Revenues		0	$ 200,000	100,000	$ 500,000
Contract assets		0		0
Deferred revenue		$ 0		$ 0