Subsequent Events - Additional Information (Details) - USD ($) $ in Thousands			1 Months Ended	12 Months Ended
	Jan. 01, 2020	Sep. 25, 2018	Feb. 26, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Number of stock options granted to employees				3,394,030	5,735,643	4,139,372
Allocated share-based compensation expense		$ 89,900		$ 60,245	$ 131,770	$ 34,986
Restricted Stock Units
Subsequent Event [Line Items]
Number of units granted to employees				6,270,720	3,911,841	2,936,437
Subsequent Event
Subsequent Event [Line Items]
Number of stock options granted to employees			2,120,230
Subsequent Event | Restricted Stock Units
Subsequent Event [Line Items]
Number of units granted to employees			3,504,514
Subsequent Event | Stock Options and Restricted Stock Units
Subsequent Event [Line Items]
Allocated share-based compensation expense			$ 84,000
2018 Equity Incentive Plan | Subsequent Event
Subsequent Event [Line Items]
Number of increased authorized shares of common stock	6,802,705
2018 Employee Stock Purchase Plan | Subsequent Event
Subsequent Event [Line Items]
Number of increased authorized shares of common stock	1,360,541