Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details)

v3.19.1
Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on fair value adjustments $ (66,970) $ 3,978
Total gain (loss) on oil & natural gas derivatives (67,260) (4,481)
Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Total gain (loss) on oil & natural gas derivatives (67,260) (4,481)
Not Designated as Hedging Instrument | Oil    
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on settlements (1,542) (8,916)
Net gain (loss) on fair value adjustments (66,827) 4,067
Total gain (loss) on oil & natural gas derivatives (68,369) (4,849)
Not Designated as Hedging Instrument | Natural gas    
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on settlements 1,252 457
Net gain (loss) on fair value adjustments (143) (89)
Total gain (loss) on oil & natural gas derivatives $ 1,109 $ 368