Marketable Securities and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Marketable Securities [Line Items]
Net unrealized gains (losses)	$ 195,000	$ 46,000	$ 1,346,000	$ 4,490,000

Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-14

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Name:	us-gaap_DebtSecuritiesTradingUnrealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration