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Summary of Net Properties and Equipment (Detail) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Property Plant And Equipment [Abstract]    
Vessels and related equipment $ 817,798 $ 850,268
Other properties and equipment 5,450 5,710
Properties and equipment, gross 823,248 855,978
Less accumulated depreciation and amortization 46,608 18,458
Net properties and equipment $ 776,640 $ 837,520