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Organization and Significant Accounting Policies (Details) - USD ($)		1 Months Ended	12 Months Ended
	Apr. 25, 2022	Apr. 30, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Organization And Significant Accounting Policies [Line Items]
Cash, cash equivalents and restricted cash			$ 108,005,000	$ 184,434,000	$ 143,583,000	$ 221,804,000
Restricted cash			7,300,000	2,400,000
Short-term investments			268,391,000	56,627,000
Long-term investments			105,872,000	245,595,000
Net increase (decrease) in cash and investments			131,100,000
Proceeds from upfront capital			60,000,000	0	$ 0
Proceeds from sale of marketable debt securities		$ 122,300,000
Intangible assets subject to amortization, impairment			0	0
Fair value of contingent consideration obligation due to discontinuation of clinical trials			$ 0	$ 0
Minimum
Organization And Significant Accounting Policies [Line Items]
Property and equipment, useful life			3 years
Maximum
Organization And Significant Accounting Policies [Line Items]
Amount insured in FDIC per account			$ 250,000
Property and equipment, useful life			7 years
Visirna Therapeutics, Inc. \| Variable Interest Entity, Primary Beneficiary
Organization And Significant Accounting Policies [Line Items]
Proceeds from upfront capital	$ 60,000,000		$ 60,000,000
GSK
Organization And Significant Accounting Policies [Line Items]
Upfront milestone payment received			120,000,000
Janssen
Organization And Significant Accounting Policies [Line Items]
Development regulatory and sales milestones payments			$ 4,900,000,000