Condensed Financial Information of Registrant Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Cash flows provided by operating activities:
Net cash provided by operating activities	$ 110,978	$ 123,658	$ 33,907
Cash flows provided by investing activities:
Net cash provided by investing activities	(61,185)	(28,197)	(32,626)
Cash flows used in financing activities:
Distributions	(25,038)	(23,744)	(23,192)
Unit repurchase	(11,088)	(4,475)	(30,817)
Net cash provided by (used in) financing activities	22,351	(64,890)	8,572
Net decrease in cash	72,144	30,571	9,853
Cash and cash equivalents at beginning of period	45,191
Cash and cash equivalents at end of period	117,335	45,191
STAR GROUP, L.P.
Cash flows provided by operating activities:
Net cash provided by operating activities	36,125	28,219	54,005
Cash flows provided by investing activities:
Net cash provided by investing activities	0	0	0
Cash flows used in financing activities:
Distributions	(25,038)	(23,744)	(23,192)
Unit repurchase	(11,088)	(4,475)	(30,817)
Net cash provided by (used in) financing activities	(36,126)	(28,219)	(54,009)
Net decrease in cash	(1)	0	(4)
Cash and cash equivalents at beginning of period	41	41	45
Cash and cash equivalents at end of period	$ 40	$ 41	$ 41