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Accounts Receivable, Net and Revenue Concentrations - Changes in the Allowance for Doubtful Accounts (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Schedule of Allowance for Doubtful Accounts      
Balance at beginning of period $ 1,064 $ 904 $ 822
Additions to costs and expenses 305 166 183
(Write-offs)/Foreign exchange effects (248) (6) (101)
Balance at end of period $ 1,121 $ 1,064 $ 904