Business Segment Information (Schedule of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Segment margin	$ 173,564	$ 170,240
Total revenues	620,009	725,808
Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	78,317	73,260
Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	275,486	285,910
Onshore Facilities & Transportation
Segment Reporting Information [Line Items]
Total revenues	209,556	317,709
Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	56,650	48,929
Operating Segments
Segment Reporting Information [Line Items]
Segment margin	173,564	170,240
Capital Expenditures	33,167	44,507
Total revenues	620,009	725,808
Operating Segments | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Segment margin	76,390	73,173
Capital Expenditures	458	654
Total revenues	78,317	73,260
Operating Segments | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Segment margin	58,639	64,391
Capital Expenditures	22,706	9,699
Total revenues	277,349	287,403
Operating Segments | Onshore Facilities & Transportation
Segment Reporting Information [Line Items]
Segment margin	25,603	21,689
Capital Expenditures	775	23,289
Total revenues	211,025	320,215
Operating Segments | Marine Transportation
Segment Reporting Information [Line Items]
Segment margin	12,932	10,987
Capital Expenditures	9,228	10,865
Total revenues	53,318	44,930
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	(1,863)	(1,493)
Intersegment | Onshore Facilities & Transportation
Segment Reporting Information [Line Items]
Total revenues	(1,469)	(2,506)
Intersegment | Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	$ 3,332	$ 3,999