Derivative Financial Instruments Gains and Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Document Period End Date					Jun. 30, 2014
Derivative cash settlement (loss) gain	$ (33,680)	[1]	$ 2,211	[1]	$ (62,620)	[1]	$ 14,003	[1]
Gain (Loss) on Derivative Instruments, Net, Pretax	(126,469)	[2]	85,190	[2]	(224,131)	[2]	54,618	[2]
Crude oil
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative cash settlement (loss) gain	(20,160)		29		(26,918)		(248)
Derivative (gain) loss	73,435		(26,044)		98,627		(22,255)
Natural Gas
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative cash settlement (loss) gain	(13,472)		(2,091)		(26,876)		7,733
Derivative (gain) loss	14,682		(50,267)		60,739		(10,198)
Natural Gas Liquids
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Derivative cash settlement (loss) gain	(48)		4,273		(8,826)		6,518
Derivative (gain) loss	$ 4,672		$ (6,668)		$ 2,145		$ (8,162)

[1] (1) Total derivative cash settlement loss (gain) is reported in the derivative cash settlement (loss) gain line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.

[2] (2) Total derivative loss (gain) is reported in the derivative loss (gain) line item on the condensed consolidated statements of cash flows within cash provided by operating activities.