Segment Reporting - Identifiable Assets by Industry Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment Reconciliation [Abstract]
Total assets	$ 313,845	$ 278,870
Reporting Segments
Segment Reconciliation [Abstract]
Total assets	313,845	278,870
Reporting Segments | Marketing
Segment Reconciliation [Abstract]
Total assets	129,876	119,370
Reporting Segments | Transportation
Segment Reconciliation [Abstract]
Total assets	51,761	34,112
Cash and other
Segment Reconciliation [Abstract]
Total assets	$ 132,208	$ 125,388