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Accounts Receivable and Sales Concentrations - Summary of Activity in the Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Receivables [Abstract]      
Balance at Beginning of Year $ 1,069 $ 1,055 $ 362
Additions 699 142 745
Write- offs (101) (59) (8)
Currency Impacts 103 (80) (28)
Balance at End of Year $ 1,719 $ 1,069 $ 1,055