Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
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, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on fair value adjustments     $ 15,608 $ (27,105)
Total gain (loss) on oil derivatives $ (14,162) $ 5,135 11,636 (11,281)
Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Total gain (loss) on oil derivatives (14,162) 5,135 11,636 (11,281)
Not Designated as Hedging Instrument | Oil        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements (1,373) 4,252 (4,213) 15,467
Net gain (loss) on fair value adjustments (12,811) 699 14,584 (26,904)
Total gain (loss) on oil derivatives (14,184) 4,951 10,371 (11,437)
Not Designated as Hedging Instrument | Natural gas        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements 159 (161) 241 357
Net gain (loss) on fair value adjustments (137) 345 1,024 (201)
Total gain (loss) on oil derivatives $ 22 $ 184 $ 1,265 $ 156