Business Combinations - Additional Information (Detail) $ in Thousands	9 Months Ended
	Jun. 30, 2017 USD ($) PartnershipUnit	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill	$ 215,262	$ 212,760
Number of heating oil dealer acquired | PartnershipUnit	3
Heating Oil Dealer, Propane Dealer and Plumbing Service Provider
Business Acquisition [Line Items]
Aggregate purchase prices partnership acquired	$ 16,000
Cash paid	14,500
Deferred liabilities	1,500
Contingent consideration	600
Aggregate purchase price allocation, intangible assets	9,300
Goodwill	2,500
Aggregate purchase price allocation, fixed assets	5,000
Gross purchase price reduced by working capital credits	$ (800)