Balance Sheet Components - Allowance for Doubtful Accounts and Reserve for Subscriber Refunds (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at the beginning of the year	$ 692	$ 315
Additions — charged to costs and expenses, or contra revenue	610	482
Deductions — recoveries of amounts previously reserved	(147)	(104)
Deductions — write-offs or refunds	(29)	(1)
Balance at end of year	1,126	692
Reserve for member refunds
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at the beginning of the year	379	530
Additions — charged to costs and expenses, or contra revenue	1,007	688
Deductions — recoveries of amounts previously reserved	0	0
Deductions — write-offs or refunds	(1,093)	(839)
Balance at end of year	$ 293	$ 379