Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Interest Rate Swaps [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period	$ 0		$ (1,614)
Included in earnings	0	[1]	(1,734)	[1]
Included in other comprehensive income (loss)	0		1,614
Settlements	0		1,734
Transfers out of Level 3 into Level 2	0		0
End of period	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
Commodity Swaps [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period	33,615		10,868
Included in earnings	24,484	[1]	20,086	[1]
Included in other comprehensive income (loss)	(11,641)		22,503
Settlements	(25,129)		(19,842)
Transfers out of Level 3 into Level 2	(21,924)		0
End of period	(595)		33,615
Total gains for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period	$ (645)		$ 244

[1] Interest rate swaps and commodity sales swaps and collars are reported in the consolidated statements of operations in interest expense, oil and gas revenues (for cash flow hedges), and gain (loss) on derivatives not designated as hedges and hedge ineffectiveness, net, respectively.