XML 68 R51.htm IDEA: XBRL DOCUMENT v3.10.0.1
Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Mar. 31, 2017
Jan. 01, 2019
Property, Plant and Equipment [Line Items]      
Extended useful life, months 30 months    
Inspection interval The majority of our vessels require certification inspections twice in every five year period    
Subsequent Event | Accounting Standards Update 2016-06      
Property, Plant and Equipment [Line Items]      
Lease assets     $ 4.5
Lease liabilities     $ 6.0
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 9 years 9 months 18 days 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