Business Segments - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Total assets:
Total assets	$ 626,340	$ 667,156
Terminalling and storage
Total assets:
Total assets	274,043	292,136
Transportation
Total assets:
Total assets	159,973	170,045
Sulfur services
Total assets:
Total assets	99,314	110,780
Natural gas liquids
Total assets:
Total assets	$ 93,010	$ 94,195