Employee Benefit Plans - Stock Activity, Weighted Average Exercise Price (Details) - Stock options outstanding - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares
Options outstanding, beginning balance (in shares)	23,013,590
Granted (in shares)	3,509,549	3,221,892	2,679,667
Exercised (in shares)	(16,159,742)
Forfeited (in shares)	(73,249)
Expired (in shares)	(5,650)
Options outstanding, end balance (in shares)	10,284,498	23,013,590
Options exercisable (in shares)	4,084,124
Options unvested (in shares)	6,200,374
Weighted Average Exercise Price
Options outstanding, beginning balance, weighted-average exercise price	$ 2.48
Granted, weighted-average exercise price	12.79
Exercised, weighted-average exercise price	2.55
Forfeited, weighted-average exercise price	6.32
Expired, weighted-average exercise price	4.78
Options outstanding, end balance, weighted-average exercise price	5.78	$ 2.48
Options exercisable, weighted-average exercise price	2.31
Options unvested, weighted-average exercise price	$ 8.07
Stock option activity additional disclosures
Options outstanding, weighted-average remaining contractual term	7 years 9 months 18 days	6 years 7 months 6 days
Options exercisable, weighted-average remaining contractual term	5 years 9 months 18 days
Options unvested, weighted-average remaining contractual term	9 years 1 month 6 days
Options outstanding, aggregate intrinsic value	$ 289,316	$ 22,277
Options exercisable, aggregate intrinsic value	129,068
Options unvested, aggregate intrinsic value	$ 160,248
Weighted-average grant date fair value of options granted (per share)	$ 7.22	$ 1.67	$ 1.55
Fair value of stock options that vested during the period	$ 5,900	$ 6,100
Compensation cost	6,800	$ 6,000	$ 6,400
Unrecognized compensation cost	$ 8,100
Period for recognition	3 years