Business Segment Information (Schedule of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Segment margin	$ 184,112	$ 173,854	$ 357,676	$ 344,094
Total revenues	634,785	752,388	1,254,794	1,478,196
Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	78,427	69,969	156,744	143,229
Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	274,606	298,881	550,092	584,791
Onshore Facilities & Transportation
Segment Reporting Information [Line Items]
Total revenues	223,046	327,353	432,602	645,062
Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	58,706	56,185	115,356	105,114
Operating Segments
Segment Reporting Information [Line Items]
Segment margin	184,112	173,854	357,676	344,094
Capital expenditures	39,363	42,391	72,530	86,898
Total revenues	634,785	752,388	1,254,794	1,478,196
Operating Segments | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Segment margin	76,528	71,602	152,918	144,775
Capital expenditures	2,521	1,447	2,979	2,101
Total revenues	78,427	69,969	156,744	143,229
Operating Segments | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Segment margin	57,705	64,542	116,344	128,933
Capital expenditures	26,137	18,560	48,843	28,259
Total revenues	276,513	300,928	553,862	588,331
Operating Segments | Onshore Facilities & Transportation
Segment Reporting Information [Line Items]
Segment margin	35,920	25,744	61,523	47,433
Capital expenditures	3,009	12,570	3,784	35,859
Total revenues	223,778	328,134	434,803	648,349
Operating Segments | Marine Transportation
Segment Reporting Information [Line Items]
Segment margin	13,959	11,966	26,891	22,953
Capital expenditures	7,696	9,814	16,924	20,679
Total revenues	56,067	53,357	109,385	98,287
Intersegment
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	(1,907)	(2,047)	(3,770)	(3,540)
Intersegment | Onshore Facilities & Transportation
Segment Reporting Information [Line Items]
Total revenues	(732)	(781)	(2,201)	(3,287)
Intersegment | Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	$ 2,639	$ 2,828	$ 5,971	$ 6,827