Inventories - Additional Information (Detail) - gal gal in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Inventory [Line Items]
Heating oil and other fuel inventories	24.2	18.4
Maximum product supply by other supplier	8.00%	8.00%
Global Companies LLC
Inventory [Line Items]
Product purchases	13.00%	13.00%
Nic Holding Corp
Inventory [Line Items]
Product purchases	8.00%	8.00%
Home heating oil and Propane
Inventory [Line Items]
Market price based product supply contracts for next twelve months	292.3
Diesel and gasoline
Inventory [Line Items]
Market price based product supply contracts for next twelve months	47.0