Segment Reporting, Identifiable Assets by Industry Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Identifiable Assets By Industry Segment [Abstract]
Assets	$ 264,163	$ 246,872
Reportable Segments [Member]
Identifiable Assets By Industry Segment [Abstract]
Assets	264,163	246,872
Reportable Segments [Member] | Marketing [Member]
Identifiable Assets By Industry Segment [Abstract]
Assets	114,526	107,257
Reportable Segments [Member] | Transportation [Member]
Identifiable Assets By Industry Segment [Abstract]
Assets	32,231	32,120
Reportable Segments [Member] | Oil and Gas [Member]
Identifiable Assets By Industry Segment [Abstract]
Assets	8,167	7,279
Reportable Segments [Member] | Other [Member]
Identifiable Assets By Industry Segment [Abstract]
Assets	$ 109,239	$ 100,216