Quarterly report pursuant to Section 13 or 15(d)

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

v2.4.0.6
Derivative Instruments and Hedging Activities (Derivatives Fair Value By Balance Sheet Location) (Details) (Not Designated as Hedging Instrument [Member], USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Derivative [Line Items]    
Derivative Asset, Fair Value, Net $ 1,511 $ 1,924
Derivative Liability, Fair Value, Net (868) (241)
Derivative, Fair Value, Net 643 1,683
Current Liabilities - Fair Market Value of Derivatives [Member] | Natural gas [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 0 0
Derivative Liability, Fair Value, Gross Liability (537) (125)
Derivative Assets (Liability), Fair Value, Gross Liability Net 537 125
Current assets - Fair market value of derivatives [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,511 1,674
Derivative Liability, Fair Value, Gross Asset 0 0
Derivative Assets (Liability), Fair Value, Gross Asset Net 1,511 1,674
Noncurrent Assets - Other Long-Term Assets [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 250
Derivative Liability, Fair Value, Gross Asset 0 0
Derivative Assets (Liability), Fair Value, Gross Asset Net 0 250
Non-current liabilities - Other long-term liabilities [Member] | Natural gas [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 0 0
Derivative Liability, Fair Value, Gross Liability (92) (116)
Derivative Assets (Liability), Fair Value, Gross Liability Net 92 116
Non-current liabilities - Other long-term liabilities [Member] | Crude oil [Member]
   
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Liability 0 0
Derivative Liability, Fair Value, Gross Liability (239) 0
Derivative Assets (Liability), Fair Value, Gross Liability Net $ 239 $ 0