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 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on fair value adjustments     $ (4,594) $ 28,555
Total gain (loss) on oil & natural gas derivatives $ (16,554) $ 10,494 (21,036) 25,797
Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Total gain (loss) on oil & natural gas derivatives (16,554) 10,494 (21,036) 25,797
Not Designated as Hedging Instrument | Oil        
Derivative Instruments, Gain (Loss) [Line Items]        
Net loss on settlements (8,131) (315) (17,049) (2,840)
Net gain (loss) on fair value adjustments (8,311) 10,128 (4,243) 27,394
Total gain (loss) on oil & natural gas derivatives (16,442) 9,813 (21,292) 24,554
Not Designated as Hedging Instrument | Natural gas        
Derivative Instruments, Gain (Loss) [Line Items]        
Net loss on settlements 151 48 607 82
Net gain (loss) on fair value adjustments (263) 633 (351) 1,161
Total gain (loss) on oil & natural gas derivatives $ (112) $ 681 $ 256 $ 1,243