Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 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]	(303)	[1]
Included in other comprehensive income (loss)	0		253
Settlements	0		303
Transfers out of Level 3 into Level 2	0		0
End of period	0		(1,361)
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	11,417	[1]	4,305	[1]
Included in other comprehensive income (loss)	2,111		(1,765)
Settlements	(11,307)		(4,040)
Transfers out of Level 3 into Level 2	(21,924)		0
End of period	13,912		9,368
Total gains for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period	$ 110		$ 265

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