Segment Data (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) Segment	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Data [Abstract]
Number of reportable segments | Segment	2
Revenues [Abstract]
Revenues	$ 496,850,000	$ 643,926,000
Segment profit (loss)	(4,011,000)	(519,772,000)
Total assets	5,788,086,000		$ 5,924,174,000
Other segment disclosures [Abstract]
Gain on disposition of assets	2,133,000	492,000
Interest expense	(10,966,000)	(12,799,000)
Loss before taxes on income	(4,011,000)	(519,772,000)
Marine Transportation [Member]
Revenues [Abstract]
Revenues	300,951,000	403,257,000
Distribution and Services [Member]
Revenues [Abstract]
Revenues	195,899,000	240,669,000
Other [Member]
Revenues [Abstract]
Segment profit (loss)	(8,862,000)	(574,206,000)
Total assets	211,688,000		357,894,000
Other segment disclosures [Abstract]
General corporate expenses	(3,820,000)	(3,348,000)
Gain on disposition of assets	2,133,000	492,000
Impairments and other charges	0	(561,274,000)
Interest expense	(10,966,000)	(12,799,000)
Other income	3,791,000	2,723,000
Loss before taxes on income	(8,862,000)	(574,206,000)
Details of "Other" total assets [Abstract]
General corporate assets	209,971,000		355,205,000
Investment in affiliates	1,717,000		2,689,000
Total other assets	211,688,000		357,894,000
Reporting Segments [Member] | Marine Transportation [Member]
Revenues [Abstract]
Revenues	300,951,000	403,257,000
Segment profit (loss)	1,940,000	50,716,000
Total assets	4,742,604,000		4,760,449,000
Other segment disclosures [Abstract]
Loss before taxes on income	1,940,000	50,716,000
Reporting Segments [Member] | Distribution and Services [Member]
Revenues [Abstract]
Revenues	195,899,000	240,669,000
Segment profit (loss)	2,911,000	3,718,000
Total assets	833,794,000		$ 805,831,000
Other segment disclosures [Abstract]
Loss before taxes on income	2,911,000	3,718,000
Intersegment Eliminations [Member]
Revenues [Abstract]
Revenues	4,903,000	10,286,000
Segment profit (loss)	490,000	1,029,000
Other segment disclosures [Abstract]
Loss before taxes on income	$ 490,000	$ 1,029,000