Major Customers And Credit Risk (Details) (Shell Oil Company [Member], Supply And Logistics Revenues [Member])	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Shell Oil Company [Member] \| Supply And Logistics Revenues [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	13.00%	12.50%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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