Balance Sheet Components - Schedule of Allowance for Sales Returns (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of period	$ (21,897)
Balance, end of period	(13,105)	$ (21,897)
Allowance for Sales Returns
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of period	(7,335)	(6,907)
Charged to revenue	(9,519)	(17,396)
Utilization of sales return/incentive reserve	12,416	16,968
Balance, end of period	$ (4,438)	$ (7,335)