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Summary of Norwegian Kroner (NOK) Denominated Borrowings Outstanding (Detail) kr in Thousands, $ in Thousands | Jun. 30, 2018 USD ($) | Dec. 31, 2017 NOK (kr) | Dec. 31, 2017 USD ($) | Mar. 31, 2017 NOK (kr) | Mar. 31, 2017 USD ($)
--- | --- | --- | --- | --- | ---
Debt [Line Items] |  |  |  |  |
Amount outstanding | $ 436,403 |  | $ 438,827 |  |
Troms Offshore Supply AS | January 2014 notes |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Amount outstanding |  | kr 212,500 | 25,965 |  |
Fair value in U.S. dollar equivalent |  |  | 25,850 |  |
Troms Offshore Supply AS | May 2012 notes |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Amount outstanding |  | kr 115,020 | 14,054 |  |
Fair value in U.S. dollar equivalent |  |  | $ 14,013 |  |
Predecessor |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Fair value in U.S. dollar equivalent |  |  |  |  | $ 280,000
Predecessor | Troms Offshore Supply AS | January 2014 notes |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Amount outstanding |  |  |  | kr 225,000 | 26,167
Fair value in U.S. dollar equivalent |  |  |  |  | 26,133
Predecessor | Troms Offshore Supply AS | May 2012 notes |  |  |  |  |
Debt [Line Items] |  |  |  |  |
Amount outstanding |  |  |  | kr 127,800 | 14,864
Fair value in U.S. dollar equivalent |  |  |  |  | $ 14,793

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