Transactions with Related Parties (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Due from related parties	$ 2,000		$ 2,000		$ 2,200
Related party transaction, revenues	3,021	$ 3,170	9,260	$ 9,236
Related party transaction, costs and expenses	247	254	746	744
ANSAC
Related Party Transaction [Line Items]
Due from related parties	63,431		63,431		$ 74,490
Related party transaction, revenues	90,433	31,774	275,167	31,774
Related party transaction, costs and expenses	1,393	$ 454	4,427	$ 454
Management Service \| Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Related party transaction, revenues	$ 2,200		$ 6,500

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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