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Derivative Instruments and Hedging Activities - Location and Fair Value Amounts of Derivative Instruments Not Qualifying as Hedging Instruments Reported in Balance Sheet (Detail) (Commodity Contracts [Member], Current Assets [Member], USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Commodity Contracts [Member] | Current Assets [Member]
   
Asset Derivatives    
Fair Value of Derivative Instruments $ 11.2us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
/ us-gaap_BalanceSheetLocationAxis
= sgy_CurrentAssetMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
$ 12.1us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
/ us-gaap_BalanceSheetLocationAxis
= sgy_CurrentAssetMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember