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
-Subparagraph (c)
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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))
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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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Sandhill Group LLC
Related Party Transaction [Line Items]
Related party transaction, revenues			$ 1,403	$ 1,488
Sandhill [Member]
Related Party Transaction [Line Items]
Related party transaction, revenues	$ 726	$ 762
Poseidon Oil Pipeline Company
Related Party Transaction [Line Items]
Related party transaction, revenues	3,044	1,980	6,066	3,956
Related party transaction, expenses	249	251	490	498
Chief Executive Officer
Related Party Transaction [Line Items]
Related party transaction, expenses	$ 165	$ 165	$ 330	$ 330
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%