Fair Value Measurement (Reconciliations Of Level 3 Fair Value Measurements) (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Commodity Swap [Member]
Beginning of period	$ 9,368				$ 10,868
Included in earnings (loss)	3,572	[1]			7,877	[1]
Included in other comprehensive income (loss)	1,847				82
Purchases, issuance and settlements	(3,038)				(7,078)
End of period	11,749				11,749
Total gains (losses) for the period included in earnings attributable to the change in unrealized gain (loss) relating to assets still held at end of period	534				799
Commodity Swaps And Collars [Member]
Beginning of period			51,439				19,948
Included in earnings (loss)			18,690	[2]			27,764	[2]
Included in other comprehensive income (loss)			(18,431)				11,912
Purchases, issuance and settlements			(18,385)				(26,311)
End of period			33,313				33,313
Total gains (losses) for the period included in earnings attributable to the change in unrealized gain (loss) relating to assets still held at end of period			305				1,453
Interest Rate Swaps [Member]
Beginning of period	(1,361)		(2,019)		(1,614)		(1,948)
Included in earnings (loss)	(1,431)	[1]	(302)	[2]	(1,734)	[1]	(609)	[2]
Included in other comprehensive income (loss)	1,361		48		1,614		(23)
Purchases, issuance and settlements	1,431		302		1,734		609
End of period	0		(1,971)		0		(1,971)
Total gains (losses) for the period included in earnings attributable to the change in unrealized gain (loss) relating to assets still held at end of period	$ 0		$ 0		$ 0		$ 0

[1] Interest rate swaps and commodity swaps are reported in the unaudited condensed consolidated statements of income in interest, net and revenues, respectively.

[2] Interest rate swaps and commodity swaps and collars are reported in the unaudited condensed consolidated statements of income in interest, net and revenues, respectively.