Amount of loss contingency liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Other Commitments [Line Items]
Contingent liabilities	$ 0
Technology License Commitments
Other Commitments [Line Items]
Milestone payments	$ 0		$ 0
Technology License Commitments \| ARO-ENaC and ARO-HIF2 Candidates
Other Commitments [Line Items]
Milestone payments		$ 2,400,000