Business Combinations - Additional Information (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2018 USD ($) PartnershipUnit	Sep. 30, 2017 USD ($) PartnershipUnit	Sep. 30, 2016 USD ($) PartnershipUnit
Business Acquisition [Line Items]
Number of dealers acquired | PartnershipUnit	6	7	4
Goodwill	$ 228,436	$ 225,915	$ 212,760
Heating Oil Dealer and Motor Fuel Dealer
Business Acquisition [Line Items]
Aggregate purchase price partnership acquired	25,200
Cash paid	23,700
Deferred liabilities	1,500
Aggregate purchase price allocation, intangible assets	15,300
Aggregate purchase price allocation, fixed assets	7,500
Gross purchase price increased (reduced) by working capital credits	$ 2,400
Heating Oil Dealer, Propane Dealer and Plumbing Service Provider
Business Acquisition [Line Items]
Aggregate purchase price partnership acquired		44,800
Cash paid		43,300
Deferred liabilities		1,500
Aggregate purchase price allocation, intangible assets		37,500
Aggregate purchase price allocation, fixed assets		10,200
Gross purchase price increased (reduced) by working capital credits		(2,900)
Contingent consideration		$ 600
Heating Oil Dealer, Motor Fuel Dealer and Propane Dealer
Business Acquisition [Line Items]
Aggregate purchase price partnership acquired			9,800
Aggregate purchase price allocation, intangible assets			5,700
Aggregate purchase price allocation, fixed assets			2,500
Gross purchase price increased (reduced) by working capital credits			(100)
Goodwill			$ 1,700