Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.2
Derivative Instruments and Hedging Activities (Fair Value of Derivative Instruments) (Details) - Not Designated as Hedging Instrument - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Derivatives, Fair Value [Line Items]    
Asset Fair Value $ 24,843 $ 65,114
Liability Fair Value (20,914) (17,920)
Net Derivative Fair Value 3,929 47,194
Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 10,679 65,114
Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (17,251) (10,480)
Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 2,339  
Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (3,663) (7,440)
Commodity - Oil | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 8,671 60,097
Commodity - Oil | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (17,251) (10,480)
Commodity - Oil | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value (8,580) 49,617
Commodity - Oil | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 2,335 0
Commodity - Oil | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (3,327) (5,672)
Commodity - Oil | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value (992) (5,672)
Commodity - Natural gas | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 2,008 5,017
Commodity - Natural gas | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value 0 0
Commodity - Natural gas | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value 2,008 5,017
Commodity - Natural gas | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 4 0
Commodity - Natural gas | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value (336) (1,768)
Commodity - Natural gas | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value (332) $ (1,768)
Contingent consideration arrangement | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 2,485  
Contingent consideration arrangement | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value 0  
Contingent consideration arrangement | Fair value of derivatives - Current    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value 2,485  
Contingent consideration arrangement | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Asset Fair Value 9,340  
Contingent consideration arrangement | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Liability Fair Value 0  
Contingent consideration arrangement | Fair value of derivatives - Non-current    
Derivatives, Fair Value [Line Items]    
Net Derivative Fair Value $ 9,340