Transactions with Related Parties (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Sandhill Group LLC
Related Party Transaction [Line Items]
Due from related parties	$ 200		$ 200		$ 200
Revenue from Related Parties			2,153	$ 2,366
Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Due from related parties	2,000		2,000		$ 1,600
Revenue from Related Parties	3,170	$ 1,979	9,236	5,935
Management Fees Revenue	2,100		6,300
Related Party Transaction, Expenses from Transactions with Related Party	254	251	744	749
ANSAC [Member]
Related Party Transaction [Line Items]
Due from related parties	59,406		59,406
Revenue from Related Parties	31,774	0	31,774	0
Related Party Transaction, Expenses from Transactions with Related Party	$ 454	$ 0	$ 454	$ 0

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.3)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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-Subparagraph (SX 210.9-03.10(3))
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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-Name Accounting Standards Codification
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