The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Transactions with Related Parties (Schedule of Transactions with Related Parties) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
ANSAC [Member]
Related Party Transaction [Line Items]
Related party transaction, revenues	$ 31,774	$ 0	$ 31,774	$ 0
Related party transaction, expenses	454	0	454	0
Sandhill Group LLC
Related Party Transaction [Line Items]
Related party transaction, revenues			2,153	2,366
Sandhill [Member]
Related Party Transaction [Line Items]
Related party transaction, revenues	750	878
Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Related party transaction, revenues	3,170	1,979	9,236	5,935
Related party transaction, expenses	254	251	744	749
Chief Executive Officer
Related Party Transaction [Line Items]
Related party transaction, expenses	$ 165	$ 165	$ 495	$ 495
Sandhill Group LLC
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	50.00%		50.00%
Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	64.00%		64.00%