Summary of Net Properties and Equipment (Detail) $ in Thousands	Dec. 31, 2018 USD ($) Vessel	Dec. 31, 2017 USD ($) Vessel
Property, Plant and Equipment [Line Items]
Vessels and related equipment	$ 1,144,028	$ 863,683
Other properties and equipment	7,455	5,710
Properties and equipment, gross	1,151,483	869,393
Less accumulated depreciation and amortization	61,626	18,458
Net properties and equipment	$ 1,089,857	$ 850,935
Number Of Vessels | Vessel	257	227
Owned Vessels in Active Service
Property, Plant and Equipment [Line Items]
Net properties and equipment	$ 914,044	$ 646,393
Number Of Vessels | Vessel	165	138
Stacked Vessels
Property, Plant and Equipment [Line Items]
Net properties and equipment	$ 169,037	$ 189,710
Number Of Vessels | Vessel	92	89
Marine Equipment and Other Assets Under Construction
Property, Plant and Equipment [Line Items]
Net properties and equipment	$ 795	$ 9,501
Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Net properties and equipment	$ 5,981	$ 5,331