Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) (Collar [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Collar [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period	$ (2,536)		$ 13,912		$ (595)		$ 33,615
Included in earnings	3,346	[1]	5,456	[1]	1,405	[1]	16,874	[1]
Included in other comprehensive income (loss)	0		(5,687)		0		(3,576)
Settlements	636		(5,551)		636		(16,859)
Transfers out of Level 3 into Level 2	0		0		0		(21,924)
End of period	1,446		8,130		1,446		8,130
Total gains for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period	$ 3,982		$ (95)		$ 2,041		$ 15

[1] Commodity collars are reported in the Unaudited Condensed Consolidated Statements of Operations in oil and natural gas revenues (for cash flow hedges) and gain (loss) on derivatives not designated as hedges and hedge ineffectiveness, net, respectively.