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Description of Business and Significant Accounting Policies (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2019
USD ($)
item
Sep. 30, 2018
USD ($)
Sep. 30, 2019
USD ($)
segment
item
Sep. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Description Of Business And Significant Accounting Policies [Line Items]          
AAA-rated money market funds $ 43,900,000   $ 43,900,000    
Number of Money Market Funds | item 5   5    
Accounts receivable, allowance $ 391,000   $ 391,000   $ 425,000
Bad Debt Expense       $ 80,000  
Number of reportable segments | segment     1    
Other income (expense)—net          
Description Of Business And Significant Accounting Policies [Line Items]          
Foreign currency (loss)/gain $ (420,000) $ (217,000) $ (612,000) $ (571,000)  
Customer concentration risk | Reseller | Total revenue          
Description Of Business And Significant Accounting Policies [Line Items]          
Concentration risk, number of resellers | item 1   1    
Concentration risk, percentage 10.00% 11.00% 10.00% 11.00%  
Customer concentration risk | Reseller | Net accounts receivable          
Description Of Business And Significant Accounting Policies [Line Items]          
Concentration risk, number of resellers | item     1    
Concentration risk, percentage     11.00%