Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Total sales	$ 236,551	$ 283,100	$ 604,115	$ 373,320	$ 183,295	$ 232,155	$ 543,063	$ 508,945	$ 1,497,086	$ 1,467,458	$ 1,753,872
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales									881,526	924,421	1,099,874
Motor fuel and other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales									322,793	261,605	366,171
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales									1,204,319	1,186,026	1,466,045
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales									110,475	101,699	101,709
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales									118,546	120,388	120,138
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales									63,746	59,345	65,980
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales									$ 292,767	$ 281,432	$ 287,827