Condensed Financial Information of Registrant Statements of Cash Flows (Detail) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Cash flows provided by operating activities:
Net cash provided by operating activities		$ 68,877	$ 175,668	$ 97,382
Cash flows provided by investing activities:
Net cash provided by investing activities		(50,326)	(28,141)	(82,166)
Cash flows used in financing activities:
Distributions		(23,448)	(24,451)	(25,593)
Unit repurchase		(42,824)	(38,431)	(51,353)
Net cash used in financing activities		(70,695)	(95,515)	(24,848)
Cash and cash equivalents at beginning of period		56,911
Cash and cash equivalents at end of period		4,767	56,911
STAR GROUP, L.P.
Cash flows provided by operating activities:
Net cash provided by operating activities	[1]	66,272	62,877	76,942
Cash flows provided by investing activities:
Net cash provided by investing activities		0	0	0
Cash flows used in financing activities:
Distributions		(23,448)	(24,451)	(25,593)
Unit repurchase		(42,824)	(38,431)	(51,353)
Net cash used in financing activities		(66,272)	(62,882)	(76,946)
Net decrease in cash			(5)	(4)
Cash and cash equivalents at beginning of period		45	50	54
Cash and cash equivalents at end of period		$ 45	$ 45	$ 50

[1] Includes distributions from subsidiaries