Quarterly report pursuant to Section 13 or 15(d)

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

v3.5.0.2
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, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on fair value adjustments     $ (27,105) $ (7,635)
Total gain (loss) on derivative contracts $ 5,135 $ 23,283 (11,281) 17,463
Crude Oil [Member] | Not Designated as Hedging Instrument [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements 4,252 9,399 15,467 23,863
Net gain (loss) on fair value adjustments 699 13,758 (26,904) (6,787)
Total gain (loss) on derivative contracts 4,951 23,157 (11,437) 17,076
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements (161) 390 357 1,235
Net gain (loss) on fair value adjustments 345 (264) (201) (848)
Total gain (loss) on derivative contracts $ 184 $ 126 $ 156 $ 387