Business Combinations - Additional Information (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2025 USD ($) PartnershipUnit	Sep. 30, 2024 USD ($) PartnershipUnit	Sep. 30, 2023 USD ($) PartnershipUnit
Business Acquisition [Line Items]
Goodwill	$ 293,350	$ 275,829	$ 262,103
Heating Oil Businesses
Business Acquisition [Line Items]
Number of businesses acquired | PartnershipUnit	1	4	2
Aggregate purchase price partnership acquired	$ 80,500	$ 49,400	$ 19,800
Aggregate purchase price allocation, intangible assets	38,700	40,400	10,400
Goodwill	17,700	13,700	8,000
Acquisition of intangible and fixed assets	7,700
Cash proceeds from sale of assets	300
Aggregate purchase price allocation, fixed assets	25,200	4,900	2,300
Gross purchase price increased (reduced) by working capital credits	$ (1,100)	$ (9,600)	$ (900)
Propane Dealers
Business Acquisition [Line Items]
Number of businesses acquired | PartnershipUnit	3	1	1