Quarterly report pursuant to Section 13 or 15(d)

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

v3.7.0.1
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, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on fair value adjustments     $ 28,555 $ (28,149)
Total gain (loss) on oil & natural gas derivatives $ 10,494 $ (15,484) 25,797 (16,416)
Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Total gain (loss) on oil & natural gas derivatives 10,494 (15,484) 25,797 (16,416)
Not Designated as Hedging Instrument | Oil        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements (315) 3,707 (2,840) 11,214
Net gain (loss) on fair value adjustments 10,128 (18,466) 27,394 (27,604)
Total gain (loss) on oil & natural gas derivatives 9,813 (14,759) 24,554 (16,390)
Not Designated as Hedging Instrument | Natural gas        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements 48 310 82 519
Net gain (loss) on fair value adjustments 633 (1,035) 1,161 (545)
Total gain (loss) on oil & natural gas derivatives $ 681 $ (725) $ 1,243 $ (26)