Weighted-Average Assumptions Used in Measurement of Partnership's Benefit Obligation (Detail)	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Weighted-Average Assumptions Used in the Measurement of the Company’s Benefit Obligation
Discount rate at year end date	5.10%	4.70%	5.85%
Expected return on plan assets for the year ended	5.10%	5.20%	4.56%

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (j)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-8

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration