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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
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.