Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Total sales	$ 283,376	$ 327,354	$ 1,517,985	$ 1,448,219
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales	115,988	169,605	1,034,554	1,025,855
Other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	94,669	86,842	272,210	220,288
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	210,657	256,447	1,306,764	1,246,143
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales	24,344	25,472	74,711	72,513
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales	32,279	30,184	87,276	81,085
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales	16,096	15,251	49,234	48,478
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales	$ 72,719	$ 70,907	$ 211,221	$ 202,076