Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities (Derivatives Designated as Hedging Instruments/ Derivatives Not Designated as Hedging Instruments) (Details)

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Derivative Instruments and Hedging Activities (Derivatives Designated as Hedging Instruments/ Derivatives Not Designated as Hedging Instruments) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]      
Net gain (loss) on derivatives, net of settlements $ (2,730) $ 1,683 $ 0
Total (loss) gain on derivative instruments included in Statement of Operations (1,360) 1,717 0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Gain (Loss) Reclassified from OCI into Income 0 1,420 (375)
Amount of Gain Recognized in Income 0 0 0
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Total (loss) gain on derivative instruments included in Statement of Operations (1,360) 1,717 0
Commodity Contract [Member] | Natural gas [Member] | Not Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Net (loss) gain on derivatives, settled (147) 34 0
Net gain (loss) on derivatives, net of settlements 229 (241) 0
Total (loss) gain on derivative instruments included in Statement of Operations 82 (207) 0
Commodity Contract [Member] | Crude Oil [Member] | Not Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Net (loss) gain on derivatives, settled 1,518 0 0
Net gain (loss) on derivatives, net of settlements (2,960) 1,924 0
Total (loss) gain on derivative instruments included in Statement of Operations $ (1,442) $ 1,924 $ 0