Equipment Acquisitions, Dispositions and Depreciation and Impairment Policies (Narrative) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) equipment	Jun. 30, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Payments to Acquire Property, Plant, and Equipment	$ 80,987	$ 155,990
Sales Price Of Equipment	19,800
Gain (Loss) on Disposition of Property Plant Equipment	13,000
Increase (Decrease) in Deferred Charges	7,720	9,003
Sale Leaseback Transaction, Net Proceeds, Investing Activities	12,500
Amortization Of Deferred Gains Included In Gains On Asset Dispositions And Impairments, Net	$ 0	1,697
Inland River Liquid Tank Barges [Member]
Property, Plant and Equipment [Line Items]
Number of Equipment Acquired | equipment	1
Inland River Towboat [Member]
Property, Plant and Equipment [Line Items]
Number of Equipment Acquired | equipment	1
Number Of Equipments Sold | equipment	1
U.S.-flag Product Tankers [Member]
Property, Plant and Equipment [Line Items]
Number of Equipment Acquired | equipment	1
U.S.-flag Harbor Tugs [Member]
Property, Plant and Equipment [Line Items]
Number of Equipment Acquired | equipment	1
Foreign-flag Harbor Tugs [Member]
Property, Plant and Equipment [Line Items]
Number of Equipment Acquired | equipment	2
Inland River Dry Cargo Barges [Member]
Property, Plant and Equipment [Line Items]
Number Of Equipments Sold | equipment	50
Sale Leaseback Transaction, Description of Asset(s)	50
Sale Leaseback Transaction, Lease Terms	84
Inland River Specialty Barges [Member]
Property, Plant and Equipment [Line Items]
Number of Equipments Removed from Service | equipment	(1)
Gain (Loss) on Asset Dispositions and Impairments, Net [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment	$ 5,300
Amortization Of Deferred Gains Included In Gains On Asset Dispositions And Impairments, Net	1,210	$ 1,210
Gain (Loss) on Asset Dispositions and Impairments, Net [Member] | Inland River Specialty Barges [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment	$ (400)