Derivative Commodity Instruments - Commodity Contracts by Business Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014 counterparty	Sep. 30, 2013	Sep. 30, 2014 counterparty	Sep. 30, 2013	Jun. 30, 2013 bbl	Mar. 31, 2013 bbl
Derivative [Line Items]
Gain (Loss) on fair value of derivatives	$ 147,735	$ (88,192)	$ 9,498	$ (51,904)
Counterparties with whom company holds net gain positions	13		13
Counterparties with whom company holds net loss positions	1		1
Derivatives Transferred to Not Designated as Hedging Instruments					2,353,000	5,078,000
Commodity contracts
Derivative [Line Items]
Gain (Loss) on fair value of derivatives	147,735	(88,192)	9,498	(51,904)
Commodity contracts | J.P Morgan Ventures
Derivative [Line Items]
Gain (Loss) on fair value of derivatives			8,500
Commodity contracts | J Aron and Company
Derivative [Line Items]
Gain (Loss) on fair value of derivatives			4,400
Commodity contracts | Bank of Montreal
Derivative [Line Items]
Gain (Loss) on fair value of derivatives			$ 3,700