Quarterly report pursuant to Section 13 or 15(d)

Equipment Acquisitions, Dispositions and Depreciation and Impairment Policies (Narrative) (Details)

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Equipment Acquisitions, Dispositions and Depreciation and Impairment Policies (Narrative) (Details)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2015
USD ($)
equipment
Jun. 30, 2014
USD ($)
Dec. 31, 2014
equipment
Property, Plant and Equipment [Line Items]      
Payments to Acquire Property, Plant, and Equipment $ 132,128 $ 273,669  
Sales Price Of Equipment 24,700    
Proceeds from disposition of property and equipment 22,686 $ 78,039  
Proceeds from Issuance of Secured Debt 2,000    
Gain (Loss) on Disposition of Property Plant Equipment $ 3,600    
Offshore Support Vessels Fast Support [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Delivered | equipment 1    
Offshore Support Vessels Supply [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Delivered | equipment     1
Wind Farm Utility Vessel [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Delivered | equipment 1    
Inland River Towboat [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Delivered | equipment 2    
Offshore Support Vessels [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Sold | equipment 2    
Asset Impairment Charges $ 6,600    
Inland River Liquid Tank Barges - 10,000 Barrel [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Sold | equipment     1
Inland River Deck Barges [Member]      
Property, Plant and Equipment [Line Items]      
Number Of Equipments Sold | equipment     12
Gains on Asset Dispositions and Impariments, Net [Member]      
Property, Plant and Equipment [Line Items]      
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property 1,600    
Amortization Of Deferred Gains Included In Gains On Asset Dispositions And Impairments, Net $ 4,600