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Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Mar. 31, 2017 | Dec. 31, 2017
Property, Plant and Equipment [Line Items] |  |
Extended useful life, months |  | 30 months
Inspection interval |  | The majority of the company's vessels require certification inspections twice in every five year period
Marine Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Percentage of salvage values |  | 7.50%
Stacked Vessels |  |
Property, Plant and Equipment [Line Items] |  |
Property plant and equipment average age | 11 years 6 months | 11 years
Minimum | Marine Equipment | From Date of Construction |  |
Property, Plant and Equipment [Line Items] |  |
Estimated useful lives, years |  | 10 years
Minimum | Other Property Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Estimated useful lives, years |  | 3 years
Maximum |  |
Property, Plant and Equipment [Line Items] |  |
Highly liquid investments, maturities |  | 3 months
Maximum | Marine Equipment | From Date of Construction |  |
Property, Plant and Equipment [Line Items] |  |
Estimated useful lives, years |  | 20 years
Maximum | Other Property Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Estimated useful lives, years |  | 10 years

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- Definition Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost. + References No definition available. + Details
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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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