Business Segment Information (Schedule of Total Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total consolidated assets	$ 5,826,326	$ 5,933,619
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Total consolidated assets	2,123,321	2,187,083
Operating Segments | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total consolidated assets	2,061,821	1,962,146
Operating Segments | Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Total consolidated assets	894,002	1,035,662
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
Total consolidated assets	703,669	711,058
Other assets
Segment Reporting Information [Line Items]
Total consolidated assets	$ 43,513	$ 37,670