Business Combinations - Additional Information (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2024 USD ($) PartnershipUnit	Sep. 30, 2023 USD ($) PartnershipUnit	Sep. 30, 2022 USD ($) PartnershipUnit
Business Acquisition [Line Items]
Goodwill	$ 275,829	$ 262,103	$ 254,110
Heating Oil Businesses
Business Acquisition [Line Items]
Number of businesses acquired | PartnershipUnit	4	2	5
Aggregate purchase price partnership acquired	$ 49,400	$ 19,800	$ 15,600
Cash and assuming			13,100
Liabilities			2,500
Aggregate purchase price allocation, intangible assets	40,400	10,400
Goodwill	13,700	8,000	3,100
Aggregate purchase price allocation, goodwill and intangible assets			7,300
Aggregate purchase price allocation, fixed assets	4,900	2,300	5,600
Gross purchase price increased (reduced) by working capital credits	$ (9,600)	$ (900)	$ (400)
Propane Dealers
Business Acquisition [Line Items]
Number of businesses acquired | PartnershipUnit	1	1