Condensed Financial Information of Registrant Statements of Cash Flows (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
STAR GROUP, L.P.
Condensed Cash Flow Statements, Captions [Line Items]
Includes distributions from subsidiaries	$ 62,877	$ 76,942	$ 52,317

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.

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