Equity Investments (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 45,755,000	[1]		$ 45,755,000	[1]
Asset Impairment Charges	35,343,000		0
OPCO [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%
Equal to property acquisitions percentage	0.50%
Appalachia Midstream JV [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%
Entity Managing Certain Surface Acreage [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%
EXCO [Member]
Schedule of Equity Method Investments [Line Items]
Equity Investment Asset Impairment Net	17,700,000
EXCO [Member] | BG Group [Member]
Schedule of Equity Method Investments [Line Items]
Contributions to equity investments	$ 100,000
TGGT Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%

[1] Our equity in TGGT and OPCO, at inception, exceeded the book value of our investments by an aggregate of $45.8 million, comprised of an aggregate $57.2 million difference in the historical basis of our contribution and the fair value of BG Group's contribution, offset by $11.4 million of goodwill included in our investment in TGGT.