Business Segments - Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Total assets:
Total assets	$ 612,199	$ 667,156
Terminalling and storage
Total assets:
Total assets	288,915	292,136
Transportation
Total assets:
Total assets	170,274	170,045
Sulfur services
Total assets:
Total assets	112,709	110,780
Natural gas liquids
Total assets:
Total assets	$ 40,301	$ 94,195