Organization and Basis of Presentation - Derivative Gains and Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net	$ 147,735	$ (88,192)	$ 9,498	$ (51,904)
Commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Open non-cash mark-to-market gains (losses) on derivative instruments	147,287	(63,560)	53,985	(48,459)
Closed gains (losses) on derivative instruments	448	(24,632)	(44,487)	(3,445)
Gain (loss) on derivative instruments, net	$ 147,735	$ (88,192)	$ 9,498	$ (51,904)