Quarterly report pursuant to Section 13 or 15(d)

Contracts Receivable and Retainage (Details)

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Contracts Receivable and Retainage (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Long-term Contracts or Programs Disclosure [Line Items]    
Contract receivable $ 31,928 $ 28,466
Allowance for bad debt 900  
Contract Receivable | Customer Concentration Risk | One Major Customer    
Long-term Contracts or Programs Disclosure [Line Items]    
Contract receivable $ 12,300  
Percentage of contract receivable 38.40%