Summary of Norwegian Kroner (NOK) Denominated Borrowings Outstanding (Parenthetical) (Detail) - Troms Offshore Supply AS	5 Months Ended	12 Months Ended
Dec. 31, 2017	Dec. 31, 2018
Notes Due January 2026
Debt [Line Items]
Debt Instrument Maturity Period	January 2026	January 2026
Notes Due May 2024
Debt [Line Items]
Debt Instrument Maturity Period	May 2024	May 2024

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentMaturityDateDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration