Subsequent Events - Additional Information (Detail) - Amazon Pipe-lay and Construction Vessel [Member] $ in Millions	Jul. 27, 2018 USD ($)
Subsequent Event [Line Items]
Capital expenditure incurred	$ 18.8
Subsequent Event [Member]
Subsequent Event [Line Items]
Capital expenditure expected	$ 57.5
Modification project payment term	12 years
Subsequent Event [Member] | Minimum [Member]
Subsequent Event [Line Items]
Cost of modification including project management and other fees and expenses	$ 260.0
Subsequent Event [Member] | Maximum [Member]
Subsequent Event [Line Items]
Cost of modification including project management and other fees and expenses	$ 290.0