Subsequent Events - Additional Information (Details) - USD ($) $ in Thousands				1 Months Ended		12 Months Ended			19 Months Ended
	Jan. 01, 2019	Sep. 25, 2018	Feb. 16, 2018	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2015
Subsequent Event [Line Items]
Earn-out payment received			$ 1,000
Stock options granted				2,225,766		5,735,643	4,139,372	5,014,600	16,700,000
Allocated share-based compensation expense		$ 89,900				$ 131,770	$ 34,986	$ 32,957
Restricted Stock Units
Subsequent Event [Line Items]
Granted				3,820,944		3,911,841	2,936,437	5,492,600
Stock Options and Restricted Stock Units
Subsequent Event [Line Items]
Allocated share-based compensation expense				$ 66,300
Subsequent Event
Subsequent Event [Line Items]
Earn-out payment received					$ 1,000
Subsequent Event | 2018 Equity Incentive Plan
Subsequent Event [Line Items]
Number of increased authorized shares of common stock	6,290,894
Subsequent Event | 2018 Employee Stock Purchase Plan
Subsequent Event [Line Items]
Number of increased authorized shares of common stock	1,258,178