Annual report pursuant to Section 13 and 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
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]      
Net gain (loss) on fair value adjustments $ 27,650us-gaap_UnrealizedGainLossOnDerivatives $ (2,730)us-gaap_UnrealizedGainLossOnDerivatives $ 1,683us-gaap_UnrealizedGainLossOnDerivatives
Total gain (loss) on derivative instruments 31,736us-gaap_GainLossOnDerivativeInstrumentsNetPretax (1,360)us-gaap_GainLossOnDerivativeInstrumentsNetPretax 1,717us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Amount of gain reclassified from OCI into income     1,420us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
Not Designated as Hedging Instrument [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Total gain (loss) on derivative instruments 31,736us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(1,360)us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
1,717us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Net gain (loss) on settlements (84)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(148)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
34us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net gain (loss) on fair value adjustments 1,267us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
230us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(241)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Total gain (loss) on derivative instruments 1,183us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
82us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(207)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 4,170us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
1,518us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
 
Net gain (loss) on fair value adjustments 26,383us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
(2,960)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
1,924us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Total gain (loss) on derivative instruments $ 30,553us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
$ (1,442)us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
$ 1,924us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_EnergyAxis
= us-gaap_CrudeOilMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember