Quarterly report pursuant to Section 13 or 15(d)

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

v3.2.0.727
Derivative Instruments and Hedging Activities (Derivatives Fair Value by Balance Sheet Location) (Details) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value $ 5,472 $ 26,601
Not Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 7,094 27,850
Liability Fair Value (1,622) (1,249)
Net Derivative Fair Value 5,472 26,601
Current assets - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 6,218 26,588
Current assets - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 671 1,262
Current liabilities - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (1,621) (1,242)
Current liabilities - Fair market value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (1) (7)
Non-current assets - Other long-term assets [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 205  
Balance Sheet Current [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value 4,597 25,346
Balance Sheet Current [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value 670 $ 1,255
Balance Sheet Non Current [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value $ 205