Segment Reporting - Summary of Segment Financial Information (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
Segment Reporting Information [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
Cost and expenses:
General and administrative expenses										30,518	28,405	25,780
Finance charge income										(4,915)	(4,576)	(5,515)
Adjusted EBITDA										136,433	111,614	96,872
(Increase) decrease in the fair value of derivative instruments	[1]									(13,390)	19,018	1,977
Depreciation and amortization expenses										35,352	31,494	32,350
Operating income		(40,943)	(19,177)	125,372	49,219	(48,559)	(12,291)	100,331	21,621	114,471	61,102	62,545
Interest expense, net										(14,323)	(11,560)	(15,532)
Amortization of debt issuance costs										(1,068)	(988)	(1,084)
Other income, net	[2]									3,822	0	0
Income before income taxes										102,902	48,554	45,929
Income tax expense										29,407	13,331	13,984
Net income		$ (28,671)	$ (16,629)	$ 85,911	$ 32,884	$ (35,086)	$ (11,044)	$ 68,374	$ 12,979	73,495	35,223	31,945
Home heating oil and propane
Segment Reporting Information [Line Items]
Total sales										1,119,777	1,081,985	1,202,194
Motor fuel and other petroleum products
Segment Reporting Information [Line Items]
Total sales										317,824	366,807	448,547
Petroleum products
Segment Reporting Information [Line Items]
Total sales										1,437,601	1,448,792	1,650,741
Equipment installations
Segment Reporting Information [Line Items]
Total sales										135,149	123,493	114,756
Services
Segment Reporting Information [Line Items]
Total sales										211,668	193,814	187,365
Installations and services
Segment Reporting Information [Line Items]
Total sales										346,817	317,307	302,121
Cost of product
Cost and expenses:
Cost and expenses										912,391	980,831	1,204,184
Cost of installations
Cost and expenses:
Cost and expenses										110,915	100,938	95,196
Cost of service
Cost and expenses:
Cost and expenses										198,246	182,506	182,731
Delivery expenses
Cost and expenses:
Cost and expenses										116,136	105,696	108,896
Operations expenses
Cost and expenses:
Cost and expenses										75,035	68,724	69,774
Garage and plant expenses
Cost and expenses:
Cost and expenses										44,889	41,822	39,746
Sales and marketing expenses
Cost and expenses:
Cost and expenses										53,790	50,126	48,144
Customer service and credit expenses
Cost and expenses:
Cost and expenses										52,027	51,230	52,578
Insurance related expenses
Cost and expenses:
Cost and expenses										39,982	41,690	35,163
Information technology expenses
Cost and expenses:
Cost and expenses										15,863	14,591	11,813
Weather hedge contracts (gain) loss
Cost and expenses:
Cost and expenses										$ 3,108	$ (7,498)	$ (12,500)

[1] Represents the change in value of unrealized open positions and expired options.

[2] See Note 2 – Summary of Significant Accounting Policies - Other Income, Net.