Quarterly report pursuant to Section 13 or 15(d)

Revenue Recognition - Narrative (Details)

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Revenue Recognition - Narrative (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Long-term Contracts or Programs Disclosure [Line Items]          
Revenue $ 54,014,000   $ 45,868,000 $ 111,304,000 $ 83,860,000
Contracts in progress 36,471,000 $ 28,373,000   36,471,000  
Advance billings on contracts 4,165,000 5,136,000   4,165,000  
Accrued contract losses 5,999,000 7,618,000   5,999,000  
Costs in Excess of Billings | Customer Concentration Risk | Three Major Customers          
Long-term Contracts or Programs Disclosure [Line Items]          
Contracts in progress 31,100,000     31,100,000  
Billings in Excess of Costs | Customer Concentration Risk | Five Major Customers          
Long-term Contracts or Programs Disclosure [Line Items]          
Customer advances 3,500,000     3,500,000  
Project, Approved Scope, Unapproved Price          
Long-term Contracts or Programs Disclosure [Line Items]          
Revenue 0   0 0 0
Shipyards          
Long-term Contracts or Programs Disclosure [Line Items]          
Revenue $ 23,620,000   $ 18,303,000 $ 42,185,000 $ 36,724,000
Reduction to estimated contract price   $ 11,700,000