Quarterly report pursuant to Section 13 or 15(d)

Balance Sheet Components - Schedule of Net Accounts Receivable Balance Concentrations by Major Category (Parenthetical) (Details)

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Balance Sheet Components - Schedule of Net Accounts Receivable Balance Concentrations by Major Category (Parenthetical) (Details)
3 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
Customer
Dec. 31, 2018
USD ($)
Customer
Accounts Notes And Loans Receivable [Line Items]    
Gross accounts receivable $ 43,593,000 $ 39,062,000
Customer Concentration Risk | Business To Business Receivables    
Accounts Notes And Loans Receivable [Line Items]    
Number of customers | Customer 1 1
Gross accounts receivable $ 18,615,000 $ 16,198,000
Credit insurance policy, deductible amount $ 400,000  
Credit insurance policy, retention percentage 10.00%  
Customer Concentration Risk | Business To Business Receivables | Maximum    
Accounts Notes And Loans Receivable [Line Items]    
Credit insurance policy, coverage limit $ 20,000,000 $ 18,000,000