Quarterly report pursuant to Section 13 or 15(d)

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Organization (Details)

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ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Organization (Details)
$ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Apr. 30, 2019
ship
vessel
Mar. 31, 2019
USD ($)
ferries
ship
vessel
towboat
segment
tug
Dec. 31, 2018
USD ($)
segment
Jan. 01, 2018
USD ($)
Property, Plant and Equipment [Line Items]        
Number of operating segments | segment   3 4  
Number of corporate non-operating segments | segment   1 1  
Number of harbor tug vessels   8    
Number of offshore vessels   2    
Number of ferries | ferries   2    
Number of towboats | towboat   2    
Number of OSVs   2    
Number of harbor tug vessels   2    
Number of ice-breaker tug vessels | tug   1    
Number of towing, salvage and rescue vessels | ship   1    
Number of additional research vessels   1    
Contract price reduction for liquidated damages | $   $ 11.2 $ 11.2  
Subsequent Event        
Property, Plant and Equipment [Line Items]        
Number of additional vessels being constructed 5      
Number of additional vessels 5      
Number of towing, salvage and rescue vessels | ship 2      
Accounting Standards Update 2014-09        
Property, Plant and Equipment [Line Items]        
Cumulative effect of new accounting pronouncement, amount of potential impact not recorded | $       $ 0.4
Cumulative effect of new accounting principle in period of adoption | $       $ 0.0