Quarterly report pursuant to Section 13 or 15(d)

Operating Leases Major Classes of Property and Equipment Earning Lease Revenues (Details)

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Operating Leases Major Classes of Property and Equipment Earning Lease Revenues (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Major Classes of Property and Equipment Earning Lease Revenues [Line Items]      
Historical cost $ 1,413,488 $ 1,407,329 $ 1,370,517
Accumulated depreciation 577,136 560,819 510,418
Net property and equipment 836,352 $ 846,510 $ 860,099
Property Subject to Operating Lease      
Major Classes of Property and Equipment Earning Lease Revenues [Line Items]      
Historical cost 530,138    
Accumulated depreciation 191,904    
Net property and equipment 338,234    
Ocean Services | Property Subject to Operating Lease      
Major Classes of Property and Equipment Earning Lease Revenues [Line Items]      
Historical cost 493,902    
Accumulated depreciation 189,469    
Net property and equipment 304,433    
Ocean Services | Property Subject to Operating Lease | Petroleum and Chemical Carriers - U.S.-flag      
Major Classes of Property and Equipment Earning Lease Revenues [Line Items]      
Historical cost 472,462    
Accumulated depreciation 187,296    
Net property and equipment 285,166    
Ocean Services | Property Subject to Operating Lease | Harbor and Offshore Tugs - U.S.-flag      
Major Classes of Property and Equipment Earning Lease Revenues [Line Items]      
Historical cost 21,440    
Accumulated depreciation 2,173    
Net property and equipment 19,267    
Inland Services | Property Subject to Operating Lease | Inland River Towboats      
Major Classes of Property and Equipment Earning Lease Revenues [Line Items]      
Historical cost 36,236    
Accumulated depreciation 2,435    
Net property and equipment $ 33,801