Stockholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands					12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Options outstanding, beginning balance (in shares)					12,210	10,370	8,467
Granted (in shares)					2,516	3,984	3,008
Exercised (in shares)					(2,650)	(1,264)	(414)
Cancelled/forfeited (in shares)					(807)	(880)	(691)
Options outstanding, ending balance (in shares)	11,269	12,210	10,370	8,467	11,269	12,210	10,370
Options vested and exercisable (in shares)								6,994
Stock Options Weighted Average Exercise Price
Options outstanding, weighted average exercise price, beginning of period (in dollars per share)	$ 4.68	$ 2.96	$ 1.92	$ 1.54	$ 4.68	$ 2.96	$ 1.92	$ 4.68	$ 2.96	$ 1.92	$ 1.54
Granted, weighted average exercise price (in dollars per share)					10.87	5.32	2.90
Exercised, weighted average exercise price (in dollars per share)					2.45	2.10	1.48
Cancelled/forfeited, weighted average exercise price (in dollars per share)					5.10	2.64	1.88
Options outstanding, weighted average exercise price, end of period (in dollars per share)	$ 4.68	$ 2.96	$ 1.92	$ 1.54	$ 4.68	$ 2.96	$ 1.92
Vested and exercisable, weighted-average exercise price (in dollars per share)								$ 2.68
Stock Option Activity, Additional Disclosures
Weighted-average remaining contractual period	7 years 3 months 18 days	7 years 9 months 18 days	8 years	8 years 6 months
Aggregate intrinsic value								$ 173,471	$ 64,590	$ 16,901	$ 7,480
Vested and exercisable, weighted average contractual term	6 years 6 months
Vested and exercisable, aggregate intrinsic value								$ 121,610
Pre-tax intrinsic value					$ 32,600	$ 3,000	$ 700
Vesting of early exercised stock options					$ 6,100	$ 3,600	$ 2,900
Weighted-average grant date fair value (in dollars per share)					$ 5.77	$ 1.78	$ 1.56