Business Segment Information (Schedule of Total Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total consolidated assets	$ 6,434,458	$ 6,597,641
Other assets
Segment Reporting Information [Line Items]
Total consolidated assets	40,158	41,217
Offshore pipeline transportation | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	2,267,552	2,306,946
Sodium Minerals & Sulfur Services | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	1,994,957	2,019,905
Onshore Facilities & Transportation | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	1,370,309	1,457,190
Marine transportation | Operating Segments
Segment Reporting Information [Line Items]
Total consolidated assets	$ 761,482	$ 772,383