Schedule of Gain (loss) on Disposition of Assets (Detail) $ in Thousands	4 Months Ended	5 Months Ended	12 Months Ended
	Jul. 31, 2017 USD ($) Vessel	Dec. 31, 2017 USD ($) Vessel	Dec. 31, 2019 USD ($) Vessel	Dec. 31, 2018 USD ($) Vessel
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Gain (losses) on vessels disposed	$ 3,561	$ 6,616	$ 2,263	$ 10,624
Number of vessels disposed | Vessel	7	11	40	38
Vessels
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Gain (losses) on vessels disposed	$ 509	$ (163)	$ 2,434	$ 10,935