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v2.4.1.9

Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
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Dec. 31, 2014 gal | Dec. 31, 2013 gal | Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Aggregated cash posted as collateral in normal course of business | 2.3 us-gaap_CashCollateralForBorrowedSecurities |  |
Hedging positions and payable amounts secured under credit facility | 28.7 us-gaap_DerivativeAmountOfHedgedItem |  | $ 14.9 us-gaap_DerivativeAmountOfHedgedItem
Call Option |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 5,600,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_OptionIndexedToIssuersEquityTypeAxis = us-gaap_CallOptionMember | 4,500,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_OptionIndexedToIssuersEquityTypeAxis = us-gaap_CallOptionMember |
Put Option |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 7,700,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_OptionIndexedToIssuersEquityTypeAxis = us-gaap_PutOptionMember | 6,900,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_OptionIndexedToIssuersEquityTypeAxis = us-gaap_PutOptionMember |
Inventory |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume |  | 1,600,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_InventoryMember |
Swap Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 12,400,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_SwapContractOneMember | 10,000,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_SwapContractOneMember |
Synthetic calls |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 94,100,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = us-gaap_SyntheticOilMember | 86,000,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = us-gaap_SyntheticOilMember |
Futures Contracts Sold |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 55,100,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_FuturesContractsTwoMember | 76,500,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_FuturesContractsTwoMember |
Corresponding Long And Short Swap Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume |  | 38,600,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_CorrespondingLongAndShortSwapContractsBoughtMember |
Hedge a Majority of its Internal Fuel Usage Swap Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 2,900,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_InternalFuelUsageSwapContractMember | 2,400,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_InternalFuelUsageSwapContractMember |
Futures Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 29,600,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_FuturesContractsOneMember | 57,600,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_FuturesContractsOneMember |
Swap Contracts Sold |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume |  | 16,300,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_SwapContractTwoMember |
Spread Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume |  | 3,900,000 us-gaap_DerivativeNonmonetaryNotionalAmountVolume / us-gaap_DerivativeByNatureAxis = sgu_SpreadContractsBoughtMember |

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- Definition Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.1) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.(a),2) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 2 -Article 7 + Details
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