Segment Reporting, Identifiable Assets by Industry Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reconciliation [Abstract]
Total assets	$ 284,508	$ 282,704
Reporting Segments
Segment Reconciliation [Abstract]
Total assets	284,508	282,704
Reporting Segments | Marketing
Segment Reconciliation [Abstract]
Total assets	135,759	134,745
Reporting Segments | Transportation
Segment Reconciliation [Abstract]
Total assets	29,422	29,069
Reporting Segments | Oil and Gas
Segment Reconciliation [Abstract]
Total assets	425	425
Cash and other assets
Segment Reconciliation [Abstract]
Total assets	$ 118,902	$ 118,465