Significant Customers (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue, Major Customer [Line Items]
Number of significant customers	2
Concentration risk, precentage of total revenues	10.00%
Export Sales Risk	3.00%
Sinclair Oil Company [Member]
Revenue, Major Customer [Line Items]
Concentration risk, precentage of total revenues	10.00%	11.00%	10.00%
Revenue for reportable segment	$ 2,018.8	$ 2,134.3	$ 2,106.6
Shell Oil Company [Member]
Revenue, Major Customer [Line Items]
Concentration risk, precentage of total revenues	11.00%	9.00%	12.00%
Revenue for reportable segment	$ 2,097.4	$ 1,830.5	$ 2,323.6