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Inventories - Additional Information (Detail) - gal gal in Millions | 12 Months Ended
--- | ---
Sep. 30, 2020 | Sep. 30, 2019
Inventory [Line Items] |  |
Heating oil and other fuel inventories | 26.9 | 22.8
Maximum product supply by other supplier |  | 10.00%
Shell Oil Company |  |
Inventory [Line Items] |  |
Percentage of product purchases from supplier | 13.00% |
Motiva Enterprises LLC |  |
Inventory [Line Items] |  |
Percentage of product purchases from supplier | 12.00% |
Global Companies LLC |  |
Inventory [Line Items] |  |
Percentage of product purchases from supplier | 11.00% |
Home heating oil and propane |  |
Inventory [Line Items] |  |
Market based product supply contracts for next twelve months | 240.5 |
Diesel and gasoline |  |
Inventory [Line Items] |  |
Market based product supply contracts for next twelve months | 44.2 |

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- Definition Heating Oil And Other Fuel Inventories + References No definition available. + Details
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Balance Type: | na
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- Definition Market based product supply contracts in gallons. + References No definition available. + Details
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- Definition Maximum Percentage Of Product Purchases + References No definition available. + Details
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- Definition Percentage of product purchases. + References No definition available. + Details
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- 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
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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_EnergyAxis=sgu_DieselAndGasolineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |