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
Mar. 31, 2017
Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on fair value adjustments $ 17,794 $ (8,648)
Total gain (loss) on derivative contracts 15,303 (932)
Crude Oil [Member] | Not Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on settlements (2,524) 7,507
Net gain (loss) on fair value adjustments 17,266 (9,137)
Total gain (loss) on derivative contracts 14,742 (1,630)
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Net gain (loss) on settlements 33 209
Net gain (loss) on fair value adjustments 528 489
Total gain (loss) on derivative contracts $ 561 $ 698