Revenue Recognition - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Revenue Recognition [Line Items]
Revenue, practical expedient, incremental cost of obtaining contract [true false]	true
Contract costs, amortization period	5 years
Contract costs, impairment loss	$ 0	$ 0	$ 0
Contract liabilities	167,200,000	170,300,000
Contract with customer liability, revenue recognized	156,800,000	139,900,000
Prepaid Expense and Other Current Assets
Revenue Recognition [Line Items]
Deferred contract costs,current	2,900,000	3,300,000
Deferred Charges and Other Assets, Net
Revenue Recognition [Line Items]
Deferred contract costs,non current	4,500,000	5,400,000
Delivery and Branch Expenses
Revenue Recognition [Line Items]
Amortization of deferred contract costs	$ 3,600,000	$ 3,800,000
Maximum
Revenue Recognition [Line Items]
Contract liabilities recognition service contract period	1 year
Equipment Maintenance Service Contracts | Maximum
Revenue Recognition [Line Items]
Revenue from service contracts period of recognition	1 year
Residential and Commercial Home Heating Oil Customers
Revenue Recognition [Line Items]
Percentage of customers receiving deliveries based on prevailing weather conditions	95.00%
Residential Customers
Revenue Recognition [Line Items]
Customer payment terms	30 days
Percentage of customers take advantage of smart pay budget payment plan	31.00%