Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Fair Value of Derivative Instruments) (Details)

v3.7.0.1
Derivative Instruments and Hedging Activities (Fair Value of Derivative Instruments) (Details) - Not Designated as Hedging Instrument [Member] - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Asset Fair Value $ 6,032 $ 103
Liability Fair Value (6,430) (18,296)
Net Derivative Fair Value (398) (18,193)
Non-current assets -Fair value of derivatives [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 2,939  
Non-current liabilities - Fair value of derivatives [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value   (28)
Non-current liabilities - Fair value of derivatives [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value   (28)
Current assets - Fair value of derivatives [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 3,093 103
Current assets - Fair value of derivatives [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 3,093 103
Current liabilities - Fair value of derivatives [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (6,430) (18,268)
Current liabilities - Fair value of derivatives [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (6,366) (17,675)
Current liabilities - Fair value of derivatives [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (64) (593)
Balance Sheet Current [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value (3,273) (17,572)
Balance Sheet Current [Member] | Natural Gas [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value (64) (593)
Balance Sheet Non Current [Member] | Crude Oil [Member]    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value $ 2,939 $ (28)