Quarterly report pursuant to Section 13 or 15(d)

Revenue from Contracts with Customers - Contract Balances (Details)

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Revenue from Contracts with Customers - Contract Balances (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Jan. 01, 2018
Dec. 31, 2017
Revenue from Contract with Customer [Abstract]      
Accounts receivable, net $ 90,378 $ 85,121 $ 85,121
Accounts receivable retainage, net 14,401 17,484 17,484
Contract Assets:      
Costs and estimated earnings in excess of billings 66,471 95,658 $ 104,852
Contract Liabilities:      
Billings in excess of cost and estimated earnings $ 39,533 $ 27,248