Inventories - Additional Information (Detail) - gal gal in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Inventory [Line Items]
Heating oil and other fuel inventories	16.3	24.2
Maximum product supply by other supplier	8.00%	8.00%
Global Companies LLC
Inventory [Line Items]
Product purchases	8.00%	13.00%
Nic Holding Corp
Inventory [Line Items]
Product purchases		8.00%
Home heating oil and Propane
Inventory [Line Items]
Market price based product supply contracts for next twelve months	287.0
Diesel and gasoline
Inventory [Line Items]
Market price based product supply contracts for next twelve months	44.8