Nature Of Operations And Accounting Policies (Schedule Of Property And Equipment By Major Classes) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,351,741	$ 1,178,556
Accumulated Depreciation	(502,544)	(444,559)
Net property and equipment	877,925	980,007
Property, Plant and Equipment, Other, Gross	849,197	733,997
Shipping Services [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	875,090	727,602
Accumulated Depreciation	(299,528)	(258,004)
Net property and equipment	575,562	469,598
Shipping Services [Member] | U.S.-flag Petroleum and Chemical Carriers [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	652,985	546,019
Accumulated Depreciation	(215,057)	(189,536)
Net property and equipment	437,928	356,483
Shipping Services [Member] | U.S.-flag Harbor Tugs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	84,155	72,877
Accumulated Depreciation	(38,984)	(34,606)
Net property and equipment	45,171	38,271
Shipping Services [Member] | Foreign-flag Harbor Tugs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	45,338	29,689
Accumulated Depreciation	(11,575)	(9,480)
Net property and equipment	33,763	20,209
Shipping Services [Member] | Ocean Liquid Tank Barge [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	39,238	39,238
Accumulated Depreciation	(13,126)	(11,604)
Net property and equipment	26,112	27,634
Shipping Services [Member] | Short-sea Container\RORO Vessels [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	20,954	20,954
Accumulated Depreciation	(8,178)	(6,774)
Net property and equipment	12,776	14,180
Shipping Services [Member] | U.S.-flag Dry bulk Carrier [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	13,000
Accumulated Depreciation	(4,733)
Net property and equipment	8,267
Shipping Services [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	19,420	18,825
Accumulated Depreciation	(7,875)	(6,004)
Net property and equipment	11,545	12,821
Inland River Services [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	445,293	419,714
Accumulated Depreciation	(181,573)	(167,127)
Net property and equipment	263,720	252,587
Inland River Services [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	20,470	18,145
Accumulated Depreciation	(8,254)	(6,658)
Net property and equipment	12,216	11,487
Inland River Services [Member] | Inland River Dry Cargo Barges [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	233,734	246,237
Accumulated Depreciation	(101,087)	(97,602)
Net property and equipment	132,647	148,635
Inland River Services [Member] | Inland River Specialty Barges [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	10,648	12,292
Accumulated Depreciation	(4,928)	(4,869)
Net property and equipment	5,720	7,423
Inland River Services [Member] | Inland River Liquid Tank Barges [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	21,802	16,114
Accumulated Depreciation	(2,684)	(1,982)
Net property and equipment	19,118	14,132
Inland River Services [Member] | Inland River Towboats
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	44,555	14,675
Accumulated Depreciation	(1,765)	(1,320)
Net property and equipment	42,790	13,355
Inland River Services [Member] | Inland River Harbor Boats [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	18,158	17,338
Accumulated Depreciation	(6,956)	(5,715)
Net property and equipment	11,202	11,623
Inland River Services [Member] | Terminal And Manufacturing Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	95,926	94,913
Accumulated Depreciation	(55,899)	(48,981)
Net property and equipment	40,027	45,932
Witt O'Brien's LLC [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,227	1,559
Accumulated Depreciation	(938)	(1,244)
Net property and equipment	289	315
Corporate And Eliminations [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	30,131	29,681
Accumulated Depreciation	(20,505)	(18,184)
Net property and equipment	$ 9,626	$ 11,497