Affiliates Balances - Additional Information (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($) Vessel	Mar. 31, 2018 USD ($) Vessel
Schedule Of Equity Method Investments [Line Items]
Total revenues	$ 122,149	$ 91,493
Sonatide Marine, Ltd.
Schedule Of Equity Method Investments [Line Items]
Due from affiliate current net after offsetting due to affiliate	63,000
Cash	$ 50,000
Number of vessels operating \| Vessel	3
Number of vessels stacked \| Vessel	1
Sonatide Marine, Ltd. \| ANGOLA
Schedule Of Equity Method Investments [Line Items]
Number of vessels operating \| Vessel	35	40
Number of vessels stacked \| Vessel	14	18
Total revenues	$ 15,000	$ 14,000
Percentage of Angolan operation revenue	13.00%	16.00%
Sonatide Marine, Ltd. \| Angola, Kwanza
Schedule Of Equity Method Investments [Line Items]
Cash	$ 20,000
Sonatide Marine, Ltd. \| Trade Accounts Receivable
Schedule Of Equity Method Investments [Line Items]
Net trade accounts receivable	$ 14,000

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