Inventories - Additional Information (Detail) - gal gal in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Inventory [Line Items]
Heating oil and other fuel inventories	19.0	26.9
Shell Oil Company
Inventory [Line Items]
Percentage of product purchases from supplier		13.00%
Motiva Enterprises LLC
Inventory [Line Items]
Percentage of product purchases from supplier	12.00%	12.00%
Global Companies LLC
Inventory [Line Items]
Percentage of product purchases from supplier	12.00%	11.00%
Home heating oil and propane
Inventory [Line Items]
Market based product supply contracts for next twelve months	215.7
Diesel and gasoline
Inventory [Line Items]
Market based product supply contracts for next twelve months	43.2