Business Segment Information (Schedule of Segment Information) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Revenues	$ 398,311,000	$ 434,447,000
Total Segment Margin	121,395,000	147,267,000
Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	108,887,000	101,990,000
Marine transportation
Segment Reporting Information [Line Items]
Revenues	80,644,000	83,574,000
Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	208,780,000	248,883,000
Operating Segments
Segment Reporting Information [Line Items]
Segment Operating Expenses	(151,834,000)	(151,913,000)
Segment Product Costs	(127,691,000)	(160,388,000)
Other Segment Items	2,609,000	25,121,000
Total Segment Margin	121,395,000	147,267,000
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Segment Operating Expenses	(32,936,000)	(27,818,000)
Segment Product Costs	0	0
Other Segment Items	597,000	23,634,000
Total Segment Margin	76,548,000	97,806,000
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
Segment Operating Expenses	(50,889,000)	(52,408,000)
Segment Product Costs	0	0
Other Segment Items	266,000	197,000
Total Segment Margin	30,021,000	31,363,000
Operating Segments | Onshore transportation and services
Segment Reporting Information [Line Items]
Segment Operating Expenses	(68,009,000)	(71,687,000)
Segment Product Costs	(127,691,000)	(160,388,000)
Other Segment Items	1,746,000	1,290,000
Total Segment Margin	$ 14,826,000	$ 18,098,000