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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