Segment Information (Schedule Of Segment Reporting Information, By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Third party revenues	$ 134,848	$ 161,228
Intersegment revenues	0	0
Total revenues	134,848	161,228
Segment profit	78,436	119,298
Equity income (loss)	(7,906)	8,545
Capital expenditures	162,257		1,001,206
Goodwill	218,256		218,256
Total assets	3,503,137		3,791,587
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Third party revenues	134,848	161,228
Intersegment revenues	0	0
Total revenues	134,848	161,228
Segment profit	78,436	119,298
Equity income (loss)	(408)	(47)
Capital expenditures	162,257		1,001,206
Goodwill	218,256		218,256
Total assets	3,503,137		3,791,587
Midstream [Member]
Segment Reporting Information [Line Items]
Third party revenues	62,924	54,182
Intersegment revenues	0	0
Total revenues	62,924	54,182
Segment profit	42,321	29,951
Equity income (loss)	(7,498)	8,592
Capital expenditures	71,521		284,288
Goodwill	0		0
Total assets	1,261,208		1,255,977
Equity Investee And Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Third party revenues	(62,924)	(54,182)
Intersegment revenues	0	0
Total revenues	(62,924)	(54,182)
Segment profit	(42,321)	(29,951)
Equity income (loss)	0	0
Capital expenditures	(71,521)		(284,288)
Goodwill	0		0
Total assets	$ (1,261,208)		$ (1,255,977)