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Allowance for Doubtful Accounts and Unbilled Services - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Receivables [Abstract]        
Provision for doubtful accounts $ 2,400 $ 3,900 $ 5,971 $ 4,344