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Commitments and Contingencies - Additional Information - Shuttle Tankers (Details)
$ in Thousands
1 Months Ended 2 Months Ended 3 Months Ended
Jun. 30, 2015
tanker
Nov. 30, 2017
vessel
Sep. 30, 2015
USD ($)
vessel
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Loss Contingencies [Line Items]          
Aggregate principal amount       $ 3,173,229 $ 3,237,703
Construction of new shuttle tankers          
Loss Contingencies [Line Items]          
Operating lease arrangement period, lessor (in years) 15 years        
Number of vessels 3   1    
Estimated cost of project     $ 370,000    
Payments made towards the commitment       277,000  
Payments due in 2018       93,200  
Undrawn borrowings       58,100  
Construction of new shuttle tankers | Long-term debt          
Loss Contingencies [Line Items]          
Aggregate principal amount       $ 250,000  
Construction of new shuttle tankers | Newbuildings          
Loss Contingencies [Line Items]          
Number of vessels | vessel   2 3