Annual report pursuant to Section 13 and 15(d)

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

v3.3.1.900
Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]      
Net gain (loss) on fair value adjustments $ (6,658) $ 27,650 $ (2,730)
Total gain (loss) on derivative contracts 28,358 31,736 (1,360)
Not Designated as Hedging Instrument [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Total gain (loss) on derivative contracts 28,358 31,736 (1,360)
Crude Oil [Member] | Not Designated as Hedging Instrument [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Net gain (loss) on settlements 33,299 4,170 1,518
Net gain (loss) on fair value adjustments (5,403) 26,383 (2,960)
Total gain (loss) on derivative contracts 27,896 30,553 (1,442)
Natural Gas [Member] | Not Designated as Hedging Instrument [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Net gain (loss) on settlements 1,717 (84) (148)
Net gain (loss) on fair value adjustments (1,255) 1,267 230
Total gain (loss) on derivative contracts $ 462 $ 1,183 $ 82