Price Risk Management Assets And Liabilities (Fair Value Of Derivative Instruments) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Total derivatives assets	$ 221,463	$ 127,625
Total derivatives liabilities	(251,361)	(97,698)
Designated as Hedging Instrument [Member]
Total derivatives assets	43,495	41,620
Total derivatives liabilities	(615)	(6,631)
Designated as Hedging Instrument [Member] | Commodity Derivatives (Margin Deposits) [Member]
Total derivatives assets	43,337	35,031
Total derivatives liabilities	(461)	(6,631)
Designated as Hedging Instrument [Member] | Commodity Derivatives [Member]
Total derivatives assets	158	6,589
Total derivatives liabilities	(154)	0
Not Designated as Hedging Instrument [Member]
Total derivatives assets	177,968	86,005
Total derivatives liabilities	(250,746)	(91,067)
Not Designated as Hedging Instrument [Member] | Commodity Derivatives (Margin Deposits) [Member]
Total derivatives assets	146,589	64,940
Total derivatives liabilities	(149,598)	(72,729)
Not Designated as Hedging Instrument [Member] | Commodity Derivatives [Member]
Total derivatives assets	815	275
Total derivatives liabilities	(2,568)	0
Not Designated as Hedging Instrument [Member] | Interest Rate Derivatives [Member]
Total derivatives assets	30,564	20,790
Total derivatives liabilities	$ (98,580)	$ (18,338)