Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Disaggregation Of Revenue [Line Items]
Total sales	$ 743,045	$ 666,032	$ 1,231,108	$ 1,194,128
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales	587,878	508,155	910,718	859,369
Other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	77,227	87,143	153,846	184,479
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	665,105	595,298	1,064,564	1,043,848
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales	28,882	26,224	66,765	60,539
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales	31,020	29,386	61,975	58,302
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales	18,038	15,124	37,804	31,439
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales	$ 77,940	$ 70,734	$ 166,544	$ 150,280