Revenue Recognition - Summary of Disaggregation of Revenue by Major Sources (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Total sales	$ 604,115	$ 543,063	$ 977,435	$ 1,052,008
Home heating oil and propane
Disaggregation Of Revenue [Line Items]
Total sales	466,401	413,466	707,213	756,812
Other petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	72,970	67,809	132,490	157,151
Petroleum products
Disaggregation Of Revenue [Line Items]
Total sales	539,371	481,275	839,703	913,963
Equipment installations
Disaggregation Of Revenue [Line Items]
Total sales	22,865	20,158	52,925	50,723
Equipment maintenance service contracts
Disaggregation Of Revenue [Line Items]
Total sales	27,045	27,764	53,913	55,672
Billable call services
Disaggregation Of Revenue [Line Items]
Total sales	14,834	13,866	30,894	31,650
Installations and services
Disaggregation Of Revenue [Line Items]
Total sales	$ 64,744	$ 61,788	$ 137,732	$ 138,045