Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation Of Revenue [Line Items]
Total sales	$ 305,618	$ 331,640	$ 1,536,726	$ 1,525,768
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales	136,146	155,161	1,046,864	1,014,530
Other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	80,012	93,840	233,858	278,319
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	216,158	249,001	1,280,722	1,292,849
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales	33,317	30,143	100,082	90,682
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales	36,888	35,164	98,863	93,466
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales	19,255	17,332	57,059	48,771
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales	$ 89,460	$ 82,639	$ 256,004	$ 232,919