Condensed Financial Information of Registrant Statements of Cash Flows (Detail) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows provided by operating activities:
Net cash provided by operating activities		$ 57,460	$ 21,058	$ 101,957
Cash flows provided by investing activities:
Net cash provided by investing activities		(65,252)	(66,381)	(19,631)
Cash flows used in financing activities:
Distributions		(25,603)	(24,322)	(23,092)
Unit repurchase		(26,714)		(12,017)
Net cash used in financing activities		(30,135)	(41,157)	(43,646)
Cash and cash equivalents at beginning of period		52,458
Cash and cash equivalents at end of period		14,531	52,458
STAR GROUP, L.P.
Cash flows provided by operating activities:
Net cash provided by operating activities	[1]	52,317	24,052	35,109
Cash flows provided by investing activities:
Net cash provided by investing activities		0	0	0
Cash flows used in financing activities:
Distributions		(25,603)	(24,322)	(23,092)
Unit repurchase		(26,714)		(12,017)
Net cash used in financing activities		(52,317)	(24,322)	(35,109)
Net decrease in cash			(270)
Cash and cash equivalents at beginning of period		54	324	324
Cash and cash equivalents at end of period		$ 54	$ 54	$ 324

[1] (a) Includes distributions from subsidiaries $52,317 $24,052 $35,109