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Accounts Receivable, Net and Revenue Concentrations - Accounts Receivable, Net (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accounts Receivable, Net, Current [Abstract]        
Trade receivables, gross $ 133,774 $ 142,299    
Allowance for doubtful accounts (1,121) (1,064) $ (904) $ (822)
Allowance for sales returns (731) (562)    
Net trade receivables 131,922 140,673    
Other 12,767 10,905    
Accounts receivable, net $ 144,689 $ 151,578