Annual report pursuant to Section 13 and 15(d)

Nature Of Operations And Accounting Policies (Estimated Useful life Of Major Assets) (Details)

v3.8.0.1
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