Business Segment Information (Schedule of Revenues by Segment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total Segment Margin	$ 607,473	$ 713,262	$ 712,758
Total revenues	1,824,655	2,480,820	2,912,770
Offshore pipeline transportation
Segment Reporting Information [Line Items]
Total revenues	237,146	318,116	284,544
Sodium minerals and sulfur services
Segment Reporting Information [Line Items]
Total revenues	877,769	1,105,987	1,174,434
Onshore facilities and transportation
Segment Reporting Information [Line Items]
Total revenues	499,482	821,072	1,233,855
Marine transportation
Segment Reporting Information [Line Items]
Total revenues	210,258	235,645	219,937
Operating Segments
Segment Reporting Information [Line Items]
Total Segment Margin	607,473	713,262	712,758
Capital Expenditures	144,324	173,042	161,393
Total revenues	1,824,655	2,480,820	2,912,770
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Total Segment Margin	270,078	320,023	285,014
Capital Expenditures	13,323	17,809	4,703
Total revenues	237,123	318,116	284,544
Operating Segments | Sodium minerals and sulfur services
Segment Reporting Information [Line Items]
Total Segment Margin	130,083	223,908	260,488
Capital Expenditures	95,511	107,837	74,712
Total revenues	886,078	1,113,623	1,181,578
Operating Segments | Onshore facilities and transportation
Segment Reporting Information [Line Items]
Total Segment Margin	147,254	111,412	119,918
Capital Expenditures	4,133	6,576	51,110
Total revenues	500,420	824,148	1,240,382
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
Total Segment Margin	60,058	57,919	47,338
Capital Expenditures	31,357	40,820	30,868
Total revenues	201,034	224,933	206,266
Intersegment
Segment Reporting Information [Line Items]
Total revenues	0	0	0
Intersegment | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Total revenues	23	0	0
Intersegment | Sodium minerals and sulfur services
Segment Reporting Information [Line Items]
Total revenues	(8,309)	(7,636)	(7,144)
Intersegment | Onshore facilities and transportation
Segment Reporting Information [Line Items]
Total revenues	(938)	(3,076)	(6,527)
Intersegment | Marine transportation
Segment Reporting Information [Line Items]
Total revenues	$ 9,224	$ 10,712	$ 13,671