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Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Accounts receivable $ 112,448 $ 103,506
Retainage 28,160 26,070
Allowance for doubtful accounts (279) (233)
Accounts receivable, net $ 140,329 $ 129,343