Annual report pursuant to Section 13 and 15(d)

Equipment Acquisitions And Dispositions (Narrative) (Details)

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Equipment Acquisitions And Dispositions (Narrative) (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
USD ($)
equipment
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Property, Plant and Equipment [Line Items]      
Capital expenditures $ 31,525 $ 37,786 $ 50,272
Sales price of equipment 16,500 2,500 16,100
Gain (loss) on disposition of property plant equipment 9,400 500 6,600
Proceeds from other long-term financial liabilities $ 33,662 0 0
Harbor Tugs - U.S.-flag      
Property, Plant and Equipment [Line Items]      
Equipment Subject to Failed Sale Leaseback, Number of Units | equipment 3    
Harbor Tugs - U.S.-flag | Minimum      
Property, Plant and Equipment [Line Items]      
Failed Sale Leaseback Transaction, Lease Terms 72    
Harbor Tugs - U.S.-flag | Maximum      
Property, Plant and Equipment [Line Items]      
Failed Sale Leaseback Transaction, Lease Terms 84    
Gains on Asset Dispositions and Impairments, Net      
Property, Plant and Equipment [Line Items]      
Amortization of deferred gains on sale of property $ 1,300 $ 2,400 $ 13,000