Transactions with Related Parties (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sandhill Group Llc [Member]
Related Party Transaction [Line Items]
Due from related parties		$ 200	$ 300
Revenue from related Parties	[1]	3,097	3,259	$ 3,060
Poseidon Oil Pipeline Company [Member]
Related Party Transaction [Line Items]
Due from related parties		1,600
Revenue from related Parties	[2]	$ 10,844	$ 4,536	$ 0

[1] We own a 50% interest in Sandhill Group, LLC.

[2] We own a 64% interest in Poseidon Oil Pipeline Company, LLC.