Related Party Transactions (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Proceeds from disposition of assets, net	$ 819,044,000	$ 313,780,000	$ 51,600,000
EFS Midstream [Member]
Cost reimbursement fixed	2,200,000	1,100,000
Cost reimbursement variable	8,400,000	1,900,000
Proceeds from disposition of assets, net		1,100,000
Gathering And Treating Fees [Member] | EFS Midstream [Member]
Related party transaction expenses paid	21,300,000	404,000
Right Of Way [Member] | EFS Midstream [Member]
Related party transaction expenses paid	$ 1,900,000