Nature Of Operations And Accounting Policies (Estimated Useful life Of Major Assets) (Details)	12 Months Ended
	Dec. 31, 2017
U.S.-flag Petroleum and Chemical Carriers [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Harbor and Offshore Tugs [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Ocean Liquid Tank Barge [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Short-sea Container\RORO Vessels [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
U.S.-flag Dry bulk Carrier [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Inland River Dry Cargo And Specialty Barges [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Inland River Liquid Tank Barges [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Inland River Towboats and Harbor Boats [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Terminal And Manufacturing Facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years