Condensed Financial Information of Registrant Statements of Cash Flows (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
STAR GROUP, L.P.
Condensed Cash Flow Statements, Captions [Line Items]
Includes distributions from subsidiaries	$ 52,317	$ 24,052	$ 35,109

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	srt_CondensedCashFlowStatementsCaptionsLineItems
Namespace Prefix:	srt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration