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v3.10.0.1

Summary of Debt Outstanding (Parenthetical) (Detail) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Troms Offshore Supply AS |  |
Debt [Line Items] |  |
Description of frequency of periodic payments on notes | semi-annually |
Weighted average interest rate of debt borrowings | 5.00% |
Troms Offshore Supply AS | Level 2 |  |
Debt [Line Items] |  |
Fair value of debt outstanding | $ 86.4 | $ 88.5
8.00% New Secured Notes Due August 2022 |  |
Debt [Line Items] |  |
Debt instrument interest rate | 8.00% |
Debt Instrument Maturity Period | August 2022 |
8.00% New Secured Notes Due August 2022 | Level 2 |  |
Debt [Line Items] |  |
Fair value of debt outstanding | $ 361.5 | $ 359.8
Norwegian Kroner Denominated Notes Due May 2024 | Troms Offshore Supply AS |  |
Debt [Line Items] |  |
Debt Instrument Maturity Period | May 2024 |
Norwegian Kroner Denominated Notes Due January 2026 | Troms Offshore Supply AS |  |
Debt [Line Items] |  |
Debt Instrument Maturity Period | January 2026 |
United States Dollar Denominated Notes Due January 2027 | Troms Offshore Supply AS |  |
Debt [Line Items] |  |
Debt Instrument Maturity Period | January 2027 |
United States Dollar Denominated Notes Due April 2027 | Troms Offshore Supply AS |  |
Debt [Line Items] |  |
Debt Instrument Maturity Period | April 2027 |

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