Business Combinations and Divestitures - Additional Information (Detail) $ in Thousands	9 Months Ended
	Jun. 30, 2025 USD ($) PartnershipUnit	Jun. 30, 2024 USD ($) PartnershipUnit	Sep. 30, 2024 USD ($)
Business Acquisition [Line Items]
Goodwill	$ 293,350		$ 275,829
Acquisition of intangible and fixed assets	$ 7,700
Heating Oil Businesses
Business Acquisition [Line Items]
Number of businesses acquired | PartnershipUnit	1	3
Cash and assuming	$ 80,500	$ 22,600
Aggregate purchase price allocation, intangible assets	38,700	14,400
Goodwill	17,700	6,300
Aggregate purchase price allocation, fixed assets	25,200	2,800
Gross purchase price increased (reduced) by working capital credits	(1,100)	$ (900)
Cash proceeds from sale of assets	$ 300
Propane Dealers
Business Acquisition [Line Items]
Number of businesses acquired | PartnershipUnit	3	1