Basis of Presentation and Accounting Policies Property and Equipment (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Capitalized Interest Costs, Including Allowance for Funds Used During Construction	$ 0.2
U.S.-flag Petroleum and Chemical Carrier [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Harbor and Offshore Tugs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Ocean Liquid Tank Barge [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Short-sea Container/RORO Vessels [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
U.S.-flag dry-bulk carrier [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Inland River Dry Cargo and Deck Barges [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Inland River Liquid Tank Barges [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Inland River Towboats [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Terminal And Manufacturing Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years