Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Gain or loss on derivative contracts) (Details)

v2.4.1.9
Derivative Instruments and Hedging Activities (Gain or loss on derivative contracts) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on fair value adjustments $ (7,914)us-gaap_UnrealizedGainLossOnDerivatives $ (1,639)us-gaap_UnrealizedGainLossOnDerivatives
Total gain (loss) on derivative instruments 2,429us-gaap_GainLossOnDerivativeInstrumentsNetPretax (2,513)us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on settlements 391us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(102)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net gain (loss) on fair value adjustments (125)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(190)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Total gain (loss) on derivative instruments 266us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(292)us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Crude Oil [Member] | Not Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on settlements 9,952us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(773)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net gain (loss) on fair value adjustments (7,789)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(1,448)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Total gain (loss) on derivative instruments $ 2,163us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
$ (2,221)us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember