Business Segments - Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Total assets:
Total assets	$ 616,979	$ 667,156
Terminalling and storage
Total assets:
Total assets	286,233	292,136
Transportation
Total assets:
Total assets	163,951	170,045
Sulfur services
Total assets:
Total assets	104,113	110,780
Natural gas liquids
Total assets:
Total assets	$ 62,682	$ 94,195