Business Segment Information (Schedule of Segment Information) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Segment Reporting Information [Line Items]
Revenues	$ 449,251,000	$ 414,001,000	$ 1,427,801,000	$ 1,189,660,000
Total Segment Margin	147,206,000	146,576,000	473,128,000	403,840,000
Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	138,632,000	143,306,000	446,060,000	377,563,000
Marine transportation
Segment Reporting Information [Line Items]
Revenues	90,064,000	77,058,000	251,052,000	237,319,000
Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	220,555,000	193,637,000	730,689,000	574,778,000
Operating Segments
Segment Reporting Information [Line Items]
Revenues	449,251,000	414,001,000	1,427,801,000	1,189,660,000
Segment Operating Expenses	(160,059,000)	(148,217,000)	(476,174,000)	(446,556,000)
Segment Product Costs	(140,484,000)	(114,837,000)	(479,293,000)	(335,007,000)
Other Segment Items	(1,502,000)	(4,371,000)	794,000	(4,257,000)
Total Segment Margin	147,206,000	146,576,000	473,128,000	403,840,000
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	137,624,000	143,250,000	442,548,000	377,265,000
Segment Operating Expenses	(38,628,000)	(36,414,000)	(123,702,000)	(105,329,000)
Segment Product Costs	0	0	0	0
Other Segment Items	(2,209,000)	(5,549,000)	(1,850,000)	(6,749,000)
Total Segment Margin	97,795,000	101,343,000	320,508,000	265,485,000
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
Revenues	90,064,000	77,058,000	251,052,000	237,319,000
Segment Operating Expenses	(61,685,000)	(51,738,000)	(169,305,000)	(152,604,000)
Segment Product Costs	0	0	0	0
Other Segment Items	301,000	250,000	499,000	693,000
Total Segment Margin	28,680,000	25,570,000	82,246,000	85,408,000
Operating Segments | Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	221,563,000	193,693,000	734,201,000	575,076,000
Operating Segments | Onshore transportation and services
Segment Reporting Information [Line Items]
Segment Operating Expenses	(59,746,000)	(60,065,000)	(183,167,000)	(188,623,000)
Segment Product Costs	(140,484,000)	(114,837,000)	(479,293,000)	(335,007,000)
Other Segment Items	406,000	928,000	2,145,000	1,799,000
Total Segment Margin	20,731,000	19,663,000	70,374,000	52,947,000
Intersegment
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	1,008,000	56,000	3,512,000	298,000
Intersegment | Marine transportation
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment | Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	$ (1,008,000)	$ (56,000)	$ (3,512,000)	$ (298,000)