Income Taxes - Reconciliation of the Federal Statutory Tax Rate to the Total Tax Provision (Benefit) (Detail)	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Federal income taxes computed at the statutory rate	21.00%	(21.00%)
State income taxes, net of federal benefit	1.40%	(11.80%)
Research & development tax refunds & credits	0.00%	(28.80%)
Dividend received deduction	(0.30%)	(6.40%)
Other, net	(0.20%)	(10.00%)
Effective income tax rate	21.90%	(78.00%)

Percentage income tax of federal statutory tax rate.

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- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-12

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- Definition

Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for dividend.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.Fact.4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

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