Segment Reporting, Identifiable Assets by Industry Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Segment Reconciliation [Abstract]
Total assets	$ 243,950	$ 246,872
Reportable segments
Segment Reconciliation [Abstract]
Total assets	243,950	246,872
Reportable segments | Marketing
Segment Reconciliation [Abstract]
Total assets	93,092	107,257
Reportable segments | Transportation
Segment Reconciliation [Abstract]
Total assets	30,348	32,120
Reportable segments | Oil and Gas (1)
Segment Reconciliation [Abstract]
Total assets	5,070	7,279
Corporate non-segment
Segment Reconciliation [Abstract]
Total assets	$ 115,440	$ 100,216