Equity method investment acquired, ownership percentage.

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Line of credit facility maximum borrowing capacity during the heating season.

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Number of customers to whom only home heating oil gasoline and diesel were sells on delivery only basis.

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Number of customers to whom sell gasoline and diesel fuel.

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Number of residential and commercial home heating oil and propane customers served.

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Number of service contracts for natural gas and other heating systems.

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- Definition

Date the original debt was scheduled to mature, in CCYY-MM-DD format.

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Face (par) amount of debt instrument at time of issuance.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

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Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP).

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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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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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The number of each class of partnership units outstanding at the balance sheet date. Units represent shares of ownership of the general, limited, and preferred partners.

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The number of units or percentage investment held in the subsidiary by the limited liability company or limited partnership.

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Organization - Additional Information (Detail) shares in Thousands		6 Months Ended
	Dec. 04, 2019 USD ($)	Mar. 31, 2021 Segment Customer Contract shares	Dec. 31, 2020 shares	Sep. 30, 2020 shares	Mar. 31, 2020 shares	Dec. 31, 2019 shares	Sep. 30, 2019 shares
Limited Partners' Capital Account [Line Items]
Number of reportable segments \| Segment		1
Fifth Amendment
Limited Partners' Capital Account [Line Items]
Non Seasonal maximum borrowing capacity under revolving credit facility \| $	$ 300,000,000
Maximum borrowing capacity (heating season December to April) under revolving credit facility \| $	$ 450,000,000
Due date of debt	Dec. 04, 2024
Fifth Amendment \| Term Loan
Limited Partners' Capital Account [Line Items]
Outstanding term loan \| $	$ 130,000,000
Senior secured term loan maturity period	5 years
Petro Holdings, Inc
Limited Partners' Capital Account [Line Items]
Ownership interest of Star Acquisitions Inc.		100.00%
Number of residential and commercial home heating oil and propane customers served \| Customer		431,200
Number of customers to whom only home heating oil, gasoline and diesel were sells on a delivery only basis \| Customer		69,500
Number of service contracts for natural gas and other heating systems \| Contract		18,300
Number of customers to whom sell gasoline and diesel fuel \| Customer		26,600
Star Group L.P.
Limited Partners' Capital Account [Line Items]
Percentage of limited partner interest		99.20%
Percentage of general partner interest		0.80%
Star Acquisitions, Inc
Limited Partners' Capital Account [Line Items]
Ownership interest of partnership		100.00%
Petroleum Heat and Power Co., Inc.
Limited Partners' Capital Account [Line Items]
Ownership interest of partnership		100.00%
Common Stock
Limited Partners' Capital Account [Line Items]
Number of outstanding units \| shares		40,199	40,737	43,328	45,622	46,404	47,685
General Partner
Limited Partners' Capital Account [Line Items]
Number of outstanding units \| shares		326	326	326	326	326	326