Business Segment Information (Schedule of Total Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
TOTAL ASSETS	$ 5,933,619	$ 6,597,641	$ 6,479,071
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
TOTAL ASSETS	2,187,083	2,306,946	2,359,013
Operating Segments | Sodium minerals and sulfur services
Segment Reporting Information [Line Items]
TOTAL ASSETS	1,962,146	2,019,905	1,844,845
Operating Segments | Onshore facilities and transportation
Segment Reporting Information [Line Items]
TOTAL ASSETS	1,035,662	1,457,190	1,431,910
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
TOTAL ASSETS	711,058	772,383	800,243
Other assets
Segment Reporting Information [Line Items]
TOTAL ASSETS	$ 37,670	$ 41,217	$ 43,060