Summary of Operations in Angola (Detail) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($) Vessel	Jun. 30, 2019 USD ($) Vessel	Jun. 30, 2020 USD ($) Vessel	Jun. 30, 2019 USD ($) Vessel
Schedule of Equity Method Investments [Line Items]
Revenues of Angolan operations (in thousands) \| $	$ 102,344	$ 125,859	$ 218,712	$ 248,008
ANGOLA
Schedule of Equity Method Investments [Line Items]
Revenues of Angolan operations (in thousands) \| $	$ 12,289	$ 14,272	$ 24,426	$ 29,670
Percent of consolidated vessel revenues	12.00%	12.00%	11.00%	12.00%
Number of company owned vessels in Angola \| Vessel	26	32	27	34
Number of stacked company owned vessels in Angola \| Vessel	9	13	10	14

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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