Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details)

v3.3.1.900
Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value $ 19,943 $ 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 19,943 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   1,262
Current liabilities - Fair value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value   (1,242)
Current liabilities - Fair value of derivatives [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value   (7)
Balance Sheet Current [Member] | Not Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 19,943 27,850
Liability Fair Value   (1,249)
Net Derivative Fair Value 19,943 26,601
Balance Sheet Current [Member] | Not Designated as Hedging Instrument [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value $ 19,943 25,346
Balance Sheet Current [Member] | Not Designated as Hedging Instrument [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value   $ 1,255