Stockholders' Equity (Deficit) - Schedule of Activity Under Equity Incentive Plan (Details) - 2008 Plan and 2017 Plan - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, Number of shares	26,336
Granted, Number of shares	1,040
Exercised, Number of shares	(10,315)
Forfeited and expired, Number of shares	(690)
Balance, Number of shares	16,371	26,336
Options exercisable at December 31, 2018, Number of shares	8,849
Balance, Weighted average exercise price	$ 4.59
Granted, Weighted average exercise price	52.32
Exercised, Weighted average exercise price	2.90
Forfeited and expired, Weighted average exercise price	6.79
Balance, Weighted average exercise price	8.59	$ 4.59
Options exercisable at December 31, 2018, Weighted average exercise price	$ 4.72
Balance, Weighted average remaining contractual life	6 years 9 months 18 days	6 years 4 months 24 days
Options exercisable at December 31, 2018, Weighted average remaining contractual life	5 years 7 months 6 days
Granted, Weighted average grant date fair value per share	$ 22.96
Outstanding, ending balance	$ 384,383
Options exercisable, ending balance	$ 230,254