Collaboration and License Agreements - Janssen Pharmaceuticals, Inc. (Details) - USD ($)		3 Months Ended		6 Months Ended
	Oct. 03, 2018	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022	Sep. 30, 2021	May 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments		$ 3,600,000,000		$ 3,600,000,000
Revenues		146,267,000	$ 151,805,000	208,813,000	$ 179,244,000
Deferred revenue		29,839,000		29,839,000		$ 74,099,000
Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 252,700,000
JJDC | Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	175,000,000
JJDC | Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock	75,000,000
Janssen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment	73,000,000
Janssen | License Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments	800,000,000
Janssen | JNJ-75220795 (ARO-JNJ1)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment							$ 10,000,000	$ 10,000,000
Revenues		0	$ 0
Contract assets		0		0
Deferred revenue		0		0
Janssen | JNJ-3989 (ARO-HBV) Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment	$ 25,000,000
Contract assets		0		0
Deferred revenue		$ 0		$ 0