Business Segment Information (Schedule of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Segment margin	$ 161,857	$ 175,819	$ 470,470	$ 533,495
Total revenues	443,125	621,697	1,371,515	1,876,491
Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	53,893	79,738	197,286	236,482
Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	206,731	277,527	642,745	827,619
Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Total revenues	130,589	205,028	360,506	637,630
Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	51,912	59,404	170,978	174,760
Operating Segments
Segment Reporting Information [Line Items]
Segment margin	161,857	175,819	470,470	533,495
Capital expenditures	28,843	42,751	100,001	115,281
Total revenues	443,125	621,697	1,371,515	1,876,491
Operating Segments | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Segment margin	57,380	81,060	217,774	233,978
Capital expenditures	2,899	1,996	5,909	4,975
Total revenues	53,870	79,738	197,263	236,482
Operating Segments | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Segment margin	27,592	55,258	89,357	171,602
Capital expenditures	19,225	26,415	67,662	75,258
Total revenues	208,909	279,416	648,987	833,278
Operating Segments | Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Segment margin	61,298	24,829	110,612	86,352
Capital expenditures	1,446	1,599	3,432	5,383
Total revenues	130,440	205,913	361,929	640,716
Operating Segments | Marine Transportation
Segment Reporting Information [Line Items]
Segment margin	15,587	14,672	52,727	41,563
Capital expenditures	5,273	12,741	22,998	29,665
Total revenues	49,906	56,630	163,336	166,015
Intersegment
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Intersegment | Offshore Pipeline Transportation
Segment Reporting Information [Line Items]
Total revenues	23	0	23	0
Intersegment | Sodium Minerals & Sulfur Services
Segment Reporting Information [Line Items]
Total revenues	(2,178)	(1,889)	(6,242)	(5,659)
Intersegment | Onshore Facilities and Transportation
Segment Reporting Information [Line Items]
Total revenues	149	(885)	(1,423)	(3,086)
Intersegment | Marine Transportation
Segment Reporting Information [Line Items]
Total revenues	$ 2,006	$ 2,774	$ 7,642	$ 8,745