Price Risk Management Assets And Liabilities (Interest Rate Swaps Outstanding) (Details) (Derivatives Not Designated As Hedging Instruments - Interest Rate Derivatives [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Fixed Interest Rate Of 2.59% [Member]
Term	May 2012	[1]
Notional Amount	$ 0		$ 350,000
Type	Forward starting to pay a fixed rate of 2.59% and receive a floating rate	[2]
Fixed rate	2.59%
Fixed Interest Rate Of 3.51% [Member]
Term	August 2012	[1]
Notional Amount	0		500,000
Type	Forward starting to pay a fixed rate of 3.51% and receive a floating rate	[2]
Fixed rate	3.51%
Fixed Interest Rate Of 4.02% [Member]
Term	July 2013	[1]
Notional Amount	400,000		300,000
Type	Forward starting to pay a fixed rate of 4.02% and receive a floating rate	[2]
Fixed rate	4.02%
Fixed Interest Rate Of 4.26 Percent [Member]
Term	July 2014	[1]
Notional Amount	400,000		0
Type	Forward starting to pay a fixed rate of 4.26% and receive a floating rate	[2]
Fixed rate	4.26%
Floating Interest Rate Of 6.70% [Member]
Term	July 2018
Notional Amount	$ 600,000		$ 500,000
Type	Pay a floating rate plus a spread of 4.17% and receive a fixed rate of 6.70%	[2]
Fixed rate	6.70%
Spread on floating rate	4.01%

[1] Represents the effective date. These forward starting swaps have a term of 10 years with a mandatory termination date the same as the effective date.

[2] (1) Floating rates are based on 3-month LIBOR.