Nature Of Operations And Accounting Policies (Estimated Useful life Of Major Assets) (Details)	12 Months Ended
	Dec. 31, 2020
Petroleum and chemical carriers - U.S.-flag
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Bulk carriers - U.S.-flag
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Harbor and offshore tugs
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Ocean liquid tank barges
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Short-sea container/RORO vessels
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Inland river dry-cargo and specialty barges
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Inland river liquid tank barges
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Inland river towboats and harbor boats
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Terminal and fleeting facilities
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years