Condensed Financial Information of Registrant of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Condensed Income Statements, Captions [Line Items]
Revenues	$ 296,644	$ 439,101	$ 782,543	$ 488,270	$ 236,551	$ 283,100	$ 604,115	$ 373,320	$ 2,006,558	$ 1,497,086	$ 1,467,458
General and administrative expenses									24,882	25,096	25,072
Operating income	(67,920)	(11,496)	117,245	22,624	(30,517)	(13,764)	119,695	54,786	60,453	130,200	92,968
Income before income taxes	(71,227)	(14,353)	114,279	20,327	(32,629)	(15,963)	117,316	52,688	49,026	121,412	76,543
Net income	$ (49,993)	$ (10,587)	$ 81,379	$ 14,489	$ (23,233)	$ (12,054)	$ 85,164	$ 37,860	35,288	87,737	55,918
STAR GROUP, L.P.
Condensed Income Statements, Captions [Line Items]
Revenues									0	0	0
General and administrative expenses									1,588	1,602	1,327
Operating income									(1,588)	(1,602)	(1,327)
Income before income taxes									(1,588)	(1,602)	(1,327)
Equity income of Star Acquisitions Inc. and subs									36,876	89,339	57,245
Net income									$ 35,288	$ 87,737	$ 55,918