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Significant Customers (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Revenue, Major Customer [Line Items]      
Number of significant customers 2    
Concentration risk, precentage of total revenues 10.00%    
Export Sales Risk 0.03    
Sinclair Oil Company [Member]      
Revenue, Major Customer [Line Items]      
Concentration risk, precentage of total revenues 8.00% 10.00% 11.00%
Revenue for reportable segment $ 1,104.9 $ 2,018.8 $ 2,134.3
Shell Oil Company [Member]      
Revenue, Major Customer [Line Items]      
Concentration risk, precentage of total revenues 9.00% 11.00% 9.00%
Revenue for reportable segment $ 1,252.6 $ 2,097.4 $ 1,830.5