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Schedule of Carrying Value of Trust Assets, Including Unrealized Gains or Losses (Detail) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017 | Jul. 31, 2017 | Mar. 31, 2017
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Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Investments held in Rabbi Trust at fair value | [1] | $ 45 | $ 8,908 |  |
Unrealized gains in fair value of trust assets |  |  | 256 |  |
Obligations under the supplemental plan |  | $ 23,797 | $ 32,508 |  |
Predecessor |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Investments held in Rabbi Trust at fair value |  |  |  |  | $ 8,759
Unrealized gains in fair value of trust assets |  |  |  | $ 82 | (95)
Obligations under the supplemental plan |  |  |  |  | $ 29,108
[1] | Tidewater converted substantially all investments held in the rabbi trust to cash to fund a lump sum benefit to the former CEO in May 2018. Refer to Note (6) for more information regarding this payment.

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- Definition Carrying amount as of the balance sheet date of assets held under deferred compensation agreements. + References 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 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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