Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Gain or loss on derivative contracts) (Details)

v3.2.0.727
Derivative Instruments and Hedging Activities (Gain or loss on derivative contracts) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on fair value adjustments     $ (21,129) $ (4,677)
Total gain (loss) on derivative instruments $ (8,249) $ (4,685) (5,820) (7,198)
Crude Oil [Member] | Not Designated as Hedging Instrument [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements 4,511 (1,569) 14,464 (2,341)
Net gain (loss) on fair value adjustments (12,755) (3,097) (20,544) (4,546)
Total gain (loss) on derivative instruments (8,244) (4,666) (6,080) (6,887)
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gain (loss) on settlements 454 (77) 845 (179)
Net gain (loss) on fair value adjustments (459) 58 (585) (132)
Total gain (loss) on derivative instruments $ (5) $ (19) $ 260 $ (311)