Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Total sales	$ 535,027	$ 436,834
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales	364,202	301,468
Other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	94,505	65,266
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	458,707	366,734
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales	29,983	27,344
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales	28,319	25,397
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales	18,018	17,359
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales	$ 76,320	$ 70,100