Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Interest Rate Swaps [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period	$ 0		$ 0		$ 0		$ (1,614)
Included in earnings	0	[1]	0	[2]	0	[1]	(1,734)	[2]
Included in other comprehensive income (loss)	0		0		0		1,614
Settlements	0		0		0		1,734
Transfers out of Level 3 into Level 2	0		0		0		0
End of period	0		0		0		0
Total gains for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period	0		0		0		0
Commodity Swaps [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period	8,130		11,749		33,615		10,868
Included in earnings	2,241	[1]	4,046	[2]	19,114	[1]	11,923	[2]
Included in other comprehensive income (loss)	(4,194)		13,182		(7,770)		13,264
Settlements	(4,574)		(3,848)		(21,432)		(10,926)
Transfers out of Level 3 into Level 2	0		0		(21,924)		0
End of period	1,603		25,129		1,603		25,129
Total gains for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period	$ (2,333)		$ 198		$ (2,318)		$ 997

[1] Commodity swaps and collars are reported in the unaudited condensed consolidated statements of income in revenues.

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