Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Total sales	$ 183,295	$ 232,155	$ 543,063	$ 508,945	$ 235,887	$ 283,376	$ 699,582	$ 535,027	$ 1,467,458	$ 1,753,872	$ 1,677,837
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales									924,421	1,099,874	1,084,827
Motor fuel and other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales									261,605	366,172	319,543
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales									1,186,026	1,466,045	1,404,370
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales									101,699	101,709	98,064
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales									120,388	120,138	111,361
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales									59,345	65,980	64,042
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales									$ 281,432	$ 287,827	$ 273,467