Segment Reporting - Identifiable Assets by Industry Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Assets	$ 296,187	$ 330,842
Operating Segments
Segment Reporting Information [Line Items]
Assets	296,187	330,842	$ 278,870
Operating Segments | Marketing
Segment Reporting Information [Line Items]
Assets	128,441	141,402	119,370
Operating Segments | Transportation
Segment Reporting Information [Line Items]
Assets	72,247	58,483	34,112
Operating Segments | Pipeline and storage
Segment Reporting Information [Line Items]
Assets	24,541	0	0
Other
Segment Reporting Information [Line Items]
Assets	$ 70,958	$ 130,957	$ 125,388