Business Segment Information (Schedule of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Segment margin	$ 156,097	$ 169,288
Total revenues	521,219	539,923
Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	64,384	78,429
Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	227,287	243,390
Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Total revenues	189,217	155,758
Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	40,331	62,346
Operating Segments
Segment Reporting Information [Line Items]
Segment margin	156,097	169,288
Capital expenditures	34,379	31,391
Total revenues	521,219	539,923
Operating Segments | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Segment margin	84,269	85,246
Capital expenditures	11,528	1,027
Total revenues	64,384	78,429
Operating Segments | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Segment margin	43,720	36,941
Capital expenditures	10,038	14,975
Total revenues	229,306	245,535
Operating Segments | Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Segment margin	20,999	28,099
Capital expenditures	1,099	1,157
Total revenues	188,150	156,799
Operating Segments | Marine Transportation
Segment Reporting Information [Line Items]
Segment margin	7,109	19,002
Capital expenditures	11,714	14,232
Total revenues	39,379	59,160
Intersegment
Segment Reporting Information [Line Items]
Total revenues	0	0
Intersegment | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	0	0
Intersegment | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	(2,019)	(2,145)
Intersegment | Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Total revenues	1,067	(1,041)
Intersegment | Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	$ 952	$ 3,186