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Collaboration and License Agreements - Janssen Pharmaceuticals, Inc - Additional Information (Detail)		3 Months Ended		6 Months Ended
	Oct. 03, 2018 USD ($) Obligation	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Jan. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		$ 151,805,000	$ 32,811,000	$ 179,244,000	$ 54,113,000
Deferred revenue		97,869,000		97,869,000			$ 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]
Agreement date	Oct. 03, 2018
Proceeds from the issuance of common stock	$ 75,000,000.0
Janssen \| Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash received as due under collaboration agreement	175,000,000.0
Janssen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments		4,900,000,000		4,900,000,000
Milestone payment	$ 73,000,000.0
Janssen \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments	$ 1,600,000,000
Janssen \| Research Collaboration and Option Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
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	$ 25,000,000.0
Number of distinct performance obligations \| Obligation	1
Revenues		0	7,500,000	0	20,200,000
Contract assets						$ 0
Deferred revenue						$ 0
Janssen \| JNJ-75220795 (ARO-JNJ1)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		100,000	$ 100,000	100,000	$ 300,000
Contract assets		100,000		100,000
Deferred revenue		$ 0		$ 0