Business Segment Information (Schedule of Total Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total consolidated assets	$ 6,560,681	$ 6,479,071
Other assets
Segment Reporting Information [Line Items]
Total consolidated assets	55,478	43,060
Offshore pipeline transportation | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	2,307,072	2,359,013
Sodium Minerals & Sulfur Services | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	1,991,392	1,844,845
Onshore Facilities & Transportation | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	1,435,504	1,431,910
Marine transportation | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	$ 771,235	$ 800,243