Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Derivatives Fair Value By Balance Sheet Location) (Details)

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Derivative Instruments and Hedging Activities (Derivatives Fair Value By Balance Sheet Location) (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Derivative [Line Items]    
Derivative Asset, Fair Value, Net $ 2,982 $ 2,499
Derivative Liability, Fair Value, Net (536) 0
Derivative, Fair Value, Net 2,446 2,499
Designated as Hedging Instrument [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Net 469 2,499
Derivative Liability, Fair Value, Net 0 0
Derivative, Fair Value, Net 469 2,499
Not Designated as Hedging Instrument [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Net 2,513 0
Derivative Liability, Fair Value, Net (536) 0
Derivative, Fair Value, Net 1,977 0
Current assets - Fair market value of derivatives [Member] | Designated as Hedging Instrument [Member] | Natural gas [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Derivative Liability, Fair Value, Gross Asset 0 0
Derivative Assets (Liability), Fair Value, Gross Asset Net 0 0
Current assets - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Natural gas [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Derivative Liability, Fair Value, Gross Asset (224) 0
Derivative Assets (Liability), Fair Value, Gross Asset Net (224) 0
Non-current assets - Other long-term assets [Member] | Designated as Hedging Instrument [Member] | Natural gas [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Derivative Liability, Fair Value, Gross Asset 0 0
Derivative Assets (Liability), Fair Value, Gross Asset Net 0 0
Non-current assets - Other long-term assets [Member] | Not Designated as Hedging Instrument [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 969 0
Derivative Liability, Fair Value, Gross Asset 0 0
Derivative Assets (Liability), Fair Value, Gross Asset Net 969 0
Current liabilities - Fair market value of derivatives [Member] | Designated as Hedging Instrument [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 469 2,499
Derivative Liability, Fair Value, Gross Liability 0 0
Derivative Assets (Liability), Fair Value, Gross Liability Net 469 2,499
Current liabilities - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 1,544 0
Derivative Liability, Fair Value, Gross Liability 0 0
Derivative Assets (Liability), Fair Value, Gross Liability Net 1,544 0
Non-current liabilities - Other long-term liabilities [Member] | Designated as Hedging Instrument [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 0 0
Derivative Liability, Fair Value, Gross Liability 0 0
Derivative Assets (Liability), Fair Value, Gross Liability Net 0 0
Non-current liabilities - Other long-term liabilities [Member] | Not Designated as Hedging Instrument [Member] | Natural gas [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 0 0
Derivative Liability, Fair Value, Gross Liability (312) 0
Derivative Assets (Liability), Fair Value, Gross Liability Net $ (312) $ 0