Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on fair value adjustments     $ (29,696) $ 15,608
Total gain (loss) on oil & natural gas derivatives $ (34,339) $ (14,162) (55,374) 11,636
Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Total gain (loss) on oil & natural gas derivatives (34,339) (14,162) (55,374) 11,636
Not Designated as Hedging Instrument | Oil        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements (9,306) (1,373) (26,353) (4,213)
Net gain (loss) on fair value adjustments (24,476) (12,811) (28,720) 14,584
Total gain (loss) on oil & natural gas derivatives (33,782) (14,184) (55,073) 10,371
Not Designated as Hedging Instrument | Natural gas        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements 67 159 675 241
Net gain (loss) on fair value adjustments (624) (137) (976) 1,024
Total gain (loss) on oil & natural gas derivatives $ (557) $ 22 $ (301) $ 1,265