Quarterly report pursuant to Section 13 or 15(d)

REVENUE, CONTRACT ASSETS AND LIABILITIES AND OTHER CONTRACT MATTERS - Narrative (Details)

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REVENUE, CONTRACT ASSETS AND LIABILITIES AND OTHER CONTRACT MATTERS - Narrative (Details)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2019
USD ($)
Jun. 30, 2019
USD ($)
vessel
Jun. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Long-term Contracts or Programs Disclosure [Line Items]          
Bad debt expense   $ 59 $ 8    
Allowance for bad debt $ 100 $ 100   $ 400  
Number of harbor tug vessels | vessel   6      
Change in estimated margins 2,300 $ 2,000      
Number of harbor tug vessels completed | vessel   4      
Reduction of estimated contract price for liquidated damages, amount 11,300 $ 11,300   $ 11,200 $ 11,200
Harbor Tug          
Long-term Contracts or Programs Disclosure [Line Items]          
Change in estimated margins 1,400 $ 1,200      
Number of harbor tug vessels completed | vessel   6      
Reserve for loss 1,600 $ 1,600      
Ice-Breaker Tug          
Long-term Contracts or Programs Disclosure [Line Items]          
Change in estimated margins 900 800      
Reserve for loss $ 100 $ 100