Stock-Based Compensation and Employee Benefit Plan - Stock Options (Additional Information) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Arrangements with Employees and Nonemployees [Abstract]
Allocated share-based compensation expense	$ 71,700,000	$ 7,700,000	$ 87,500,000	$ 22,300,000
Capitalized stock-based compensation costs	0	0	0	0
Stock options exercised	2,900,000	600,000	8,800,000	3,100,000
Unrecognized compensation cost related to unvested stock options	$ 64,900,000		$ 64,900,000
Expense expected to be recognized over remaining weighted-average period			2 years 9 months 3 days
Excess tax benefits		$ 0	$ 0	$ 0
Class A common stock
Share-based Arrangements with Employees and Nonemployees [Abstract]
Granted options (in shares)	1,600,526	0	1,600,526	0
Class B common stock
Share-based Arrangements with Employees and Nonemployees [Abstract]
Granted options (in shares)	14,828,664	113,612	15,252,524	1,795,296