Equity method investment acquired, ownership percentage.

No definition available.

Name:	sgu_EquityMethodInvestmentAcquiredOwnershipPercentage
Namespace Prefix:	sgu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	sgu_LineOfCreditFacilityMaximumBorrowingCapacityDuringHeatingSeason
Namespace Prefix:	sgu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	sgu_NumberOfCustomersToWhomOnlyHomeHeatingOilGasolineAndDieselWereSellsOnDeliveryOnlyBasis
Namespace Prefix:	sgu_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of customers to whom sell gasoline and diesel fuel.

+ References

No definition available.

+ Details

Name:	sgu_NumberOfCustomersToWhomSellGasolineAndDieselFuel
Namespace Prefix:	sgu_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	sgu_NumberOfResidentialAndCommercialHomeHeatingOilAndPropaneCustomersServed
Namespace Prefix:	sgu_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	sgu_NumberOfServiceContractsForNaturalGasAndOtherHeatingSystems
Namespace Prefix:	sgu_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

+ Details

Name:	us-gaap_DebtConversionOriginalDebtDueDateOfDebtDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_LimitedPartnersCapitalAccountLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8672-108599

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(a))
-URI http://asc.fasb.org/extlink&oid=120401414&loc=d3e603758-122996

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(b))
-URI http://asc.fasb.org/extlink&oid=120401414&loc=d3e603758-122996

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187171-122770

+ Details

Name:	us-gaap_PartnersCapitalAccountUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_SubsidiaryOfLimitedLiabilityCompanyOrLimitedPartnershipOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=sgu_FifthAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=sgu_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=sgu_StarGroupLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=sgu_SubsidiariesTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=sgu_SubsidiariesFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_GeneralPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Organization - Additional Information (Detail) shares in Thousands		3 Months Ended
	Dec. 04, 2019 USD ($)	Dec. 31, 2020 Segment Customer Contract shares	Sep. 30, 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		434,800
Number of customers to whom only home heating oil, gasoline and diesel were sells on a delivery only basis \| Customer		66,800
Number of service contracts for natural gas and other heating systems \| Contract		18,200
Number of customers to whom sell gasoline and diesel fuel \| Customer		26,400
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		40,737	43,328	46,404	47,685
General Partner
Limited Partners' Capital Account [Line Items]
Number of outstanding units \| shares		326	326	326	326