Equity Investments (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Equity investments in unconsolidated affiliates	$ 188,772,000		$ 188,772,000		$ 187,031,000
Payments of distributions to affiliates			1,593,000	8,132,000
Equity in earnings of investments	5,887,000	1,656,000	11,537,000	6,711,000
Deepwater Gateway, L.L.C. [Member]
Equity method investment, ownership percentage	50.00%		50.00%
Equity investments in unconsolidated affiliates	98,300,000		98,300,000		99,800,000
Capitalized interest	1,400,000		1,400,000		1,500,000
Payments of distributions to affiliates	1,800,000		3,600,000
Independence Hub, LLC [Member]
Equity method investment, ownership percentage	20.00%		20.00%
Equity investments in unconsolidated affiliates	81,000,000		81,000,000		82,400,000
Capitalized interest	5,100,000		5,100,000		5,200,000
Payments of distributions to affiliates	5,200,000		9,600,000
Clough Helix JV [Member]
Equity method investment, ownership percentage	50.00%		50.00%
Equity investments in unconsolidated affiliates	9,500,000		9,500,000		4,900,000
Equity in earnings of investments	$ 700,000	$ (4,300,000)	$ 1,100,000	$ (5,700,000)