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Summary of Significant Accounting Policies - Current and Long-Term Accounts and Notes Receivable and Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Accounting Policies [Abstract]    
Allowances for doubtful accounts on current receivable $ 5,090 $ 4,465
Current retainage balances 277,700 300,500
Non-current retainage balances 69,900 41,900
Unbilled receivables $ 387,900 $ 303,900