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Summary of Vessels and ROVs Impaired, Amount of Impairment Incurred and Combined Fair Value of Assets after Impairment Charges (Parenthetical) (Detail) - USD ($) | 3 Months Ended | 4 Months Ended | 5 Months Ended | 12 Months Ended
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Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Jul. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2018 | Mar. 31, 2017
Schedule of Vessels Impaired and Amount of Impairment Incurred [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairments Charges | $ 36,878,000 | $ 16,853,000 | $ 1,215,000 | $ 6,186,000 | $ 16,777,000 |  | $ 16,777,000 | [1] | $ 61,132,000 | [1] |
Inventory and Other Non-vessel Assets |  |  |  |  |  |  |  |  |  |  |
Schedule of Vessels Impaired and Amount of Impairment Incurred [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairments Charges |  |  |  |  |  |  | $ 2,300,000 |  | $ 3,500,000 |  | $ 2,200,000
Non-vessel Assets |  |  |  |  |  |  |  |  |  |  |
Schedule of Vessels Impaired and Amount of Impairment Incurred [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairments Charges |  |  |  |  |  | $ 0 |  |  |  |  |
[1] | The twelve months ended December 31, 2018, the period August 1, 2017 through December 31, 2017 and the twelve months ended March 31, 2017 included $3.5 million, $2.3 million and $2.2 million respectively, of impairments related to inventory and other non-vessel assets. There were no impairments to non-vessel assets during the period April 1, 2017 through July 31, 2017.

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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228 + Details
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