Investments in Unconsolidated Affiliates - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2003
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Significant Property, Plant and Equipment Owned by Equity Method Investee	75.00%
Equity Method Investments	$ 49,607,000	$ 51,820,000	$ 58,736,000
Equity Method Investment, Percentage of Cumulative Undistributed Earnings	50.00%
Medusa Spar LLC Investment [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of equity method investment	50.00%
Equity Method Investment, Aggregate Cost				43,700,000
Equity Method Investment, Significant Property, Plant and Equipment Owned by Equity Method Investee	75.00%
Equity Method Investment, Significant Property, Plant and Equipment Owned by Equity Method Investee, Percentage Financed by Debt	50.00%
Equity Method Investment, Significant Property, Plant and Equipment Owned by Equity Method Investee, Percentage Financed by Equity	50.00%
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	49,500,000
Equity Method Investments	49,480,000	51,820,000	57,388,000
Retained Earnings, Undistributed Earnings from Equity Method Investees	7,800,000	10,200,000
Equity Method Investment, Dividends or Distributions	$ 6,300,000	$ 7,700,000	$ 8,500,000