Business Segment Information (Schedule of Total Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total consolidated assets	$ 5,949,613	$ 5,933,619
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Total consolidated assets	2,169,156	2,187,083
Operating Segments | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total consolidated assets	1,958,893	1,962,146
Operating Segments | Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Total consolidated assets	1,065,316	1,035,662
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
Total consolidated assets	715,404	711,058
Other assets
Segment Reporting Information [Line Items]
Total consolidated assets	$ 40,844	$ 37,670