Revenue Recognition (Narrative) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reset tariff period for transportation contracts	1 year
Expected duration of performance obligations	1 year
Offshore Pipeline Transportation \| Fixed-price Contract
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated aggregate transaction price of unsatisfied performance obligations	$ 379,915
Marine Transportation \| M/T American Phoenix \| Fixed-price Contract
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated aggregate transaction price of unsatisfied performance obligations	67,488
Onshore Facilities & Transportation \| Fixed-price Contract
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated aggregate transaction price of unsatisfied performance obligations	$ 202,726

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- Definition

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+ References

No definition available.

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- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130556-203045

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- Definition

Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130556-203045

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

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