Commitments And Contingencies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) equipment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 claim	Dec. 31, 2012 claim	Dec. 31, 2010 claim	Sep. 30, 2016 USD ($)
Commitments and Contingencies [Line Items]
Unrecorded unconditional purchase obligation	$ 8,461
Unrecorded Unconditional Purchase Obligation, Due in Remainder of Fiscal Year	7,849
Unrecorded Unconditional Purchase Obligation, Due within Two Years	612
Total rental expense for operating leases	$ 42,800	$ 35,200	$ 35,400
U.S.-flag Harbor Tugs [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Maximum Quantity | equipment	2
Number of equipment leases | equipment	8
Pure Car/Truck Carriers [Member]
Commitments and Contingencies [Line Items]
Number of equipment leases | equipment	4
Inland River Dry Cargo Barges [Member]
Commitments and Contingencies [Line Items]
Number of equipment leases | equipment	50
Inland River Towboats
Commitments and Contingencies [Line Items]
Number of equipment leases | equipment	4
Inland River Harbor Boats [Member]
Commitments and Contingencies [Line Items]
Number of equipment leases | equipment	6
U.S.-flag Petroleum and Chemical Carriers [Member]
Commitments and Contingencies [Line Items]
Number of equipment leases | equipment	3
Minimum [Member]
Commitments and Contingencies [Line Items]
Lessee, Operating Lease, Term of Contract	1 month
Minimum [Member] | U.S.-flag Petroleum and Chemical Carriers [Member]
Commitments and Contingencies [Line Items]
Sale Leaseback Transaction, Lease Terms	57
Maximum [Member]
Commitments and Contingencies [Line Items]
Sale Leaseback Transaction, Lease Terms		76	84
Lessee, Operating Lease, Term of Contract	15 years
Maximum [Member] | Inland River Dry Cargo Barges [Member]
Commitments and Contingencies [Line Items]
Sale Leaseback Transaction, Lease Terms	84
Maximum [Member] | U.S.-flag Petroleum and Chemical Carriers [Member]
Commitments and Contingencies [Line Items]
Sale Leaseback Transaction, Lease Terms	104
Multi-district Litigation [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | claim						1
Loss Contingency, Number of Plaintiffs		11
Abney Litigation [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | claim					668
Abood Litigation [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | claim				174
Shipping Services [Member]
Commitments and Contingencies [Line Items]
Unrecorded unconditional purchase obligation	$ 5,400
Unrecorded Unconditional Purchase Obligation, Due in Remainder of Fiscal Year	5,400
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Inland River Services [Member]
Commitments and Contingencies [Line Items]
Unrecorded unconditional purchase obligation	3,061
Unrecorded Unconditional Purchase Obligation, Due in Remainder of Fiscal Year	2,449
Unrecorded Unconditional Purchase Obligation, Due within Two Years	$ 612
American Maritime Officers Pension Plan [Member] | Pension Plan
Commitments and Contingencies [Line Items]
Multiemployer Plans, Withdrawal Obligation							$ 28,600