Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Disaggregation Of Revenue [Line Items]
Total sales	$ 247,692	$ 305,618	$ 743,045	$ 488,063	$ 240,331	$ 331,640	$ 666,032	$ 528,096	$ 1,784,418	$ 1,766,099	$ 1,952,862
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales									1,119,777	1,081,985	1,202,194
Motor fuel and other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales									317,824	366,807	448,547
Petroleum Products
Disaggregation Of Revenue [Line Items]
Total sales									1,437,601	1,448,792	1,650,741
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales									135,149	123,493	114,756
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales									136,042	129,478	126,887
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales									75,626	64,336	60,478
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales									$ 346,817	$ 317,307	$ 302,121