Business Segment Information (Schedule of Segment Information) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Revenues	$ 446,555,000	$ 398,311,000
Total Segment Margin	156,440,000	121,395,000
Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	147,281,000	108,887,000
Marine transportation
Segment Reporting Information [Line Items]
Revenues	80,045,000	80,644,000
Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	219,229,000	208,780,000
Operating Segments
Segment Reporting Information [Line Items]
Revenues	446,555,000
Segment Operating Expenses	(153,416,000)	(151,834,000)
Segment Product Costs	(140,093,000)	(127,691,000)
Other Segment Items	3,394,000	2,609,000
Total Segment Margin	156,440,000	121,395,000
Operating Segments | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	147,416,000
Segment Operating Expenses	(43,170,000)	(32,936,000)
Segment Product Costs	0	0
Other Segment Items	2,977,000	597,000
Total Segment Margin	107,088,000	76,548,000
Operating Segments | Marine transportation
Segment Reporting Information [Line Items]
Revenues	80,045,000
Segment Operating Expenses	(52,121,000)	(50,889,000)
Segment Product Costs	0	0
Other Segment Items	(7,000)	266,000
Total Segment Margin	27,917,000	30,021,000
Operating Segments | Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	219,094,000
Operating Segments | Onshore transportation and services
Segment Reporting Information [Line Items]
Segment Operating Expenses	(58,125,000)	(68,009,000)
Segment Product Costs	(140,093,000)	(127,691,000)
Other Segment Items	424,000	1,746,000
Total Segment Margin	21,435,000	$ 14,826,000
Intersegment
Segment Reporting Information [Line Items]
Revenues	0
Intersegment | Offshore pipeline transportation
Segment Reporting Information [Line Items]
Revenues	(135,000)
Intersegment | Marine transportation
Segment Reporting Information [Line Items]
Revenues	0
Intersegment | Onshore transportation and services
Segment Reporting Information [Line Items]
Revenues	$ 135,000