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Balance Sheet Components - Allowance for Doubtful Accounts and Reserve for Subscriber Refunds (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Allowance for doubtful accounts      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at the beginning of the year $ 315 $ 295 $ 384
Additions — charged to costs and expenses, or contra revenue, net 482 158 107
Deductions — recoveries of amounts previously charged-off (104) (125) (89)
Deductions — write-offs (1) (13) (107)
Balance at end of year 692 315 295
Reserve for member refunds      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at the beginning of the year 530 474 530
Additions — charged to costs and expenses, or contra revenue, net 688 942 507
Deductions — recoveries of amounts previously charged-off 0 0 0
Deductions — write-offs (839) (886) (563)
Balance at end of year $ 379 $ 530 $ 474