Stock-Based Compensation and Employee Benefit Plan - Stock-bases Compensation and Stock Options (Additional Information) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Arrangements with Employees and Nonemployees [Abstract]
Allocated share-based compensation expense		$ 180,300,000	$ 30,500,000	$ 28,200,000
Capitalized stock-based compensation costs	$ 0	0	0
Stock options exercised		9,200,000	3,400,000	2,600,000
Unrecognized compensation cost related to unvested stock options		$ 70,400,000	$ 62,400,000
Expense expected to be recognized over remaining weighted-average period		2 years 9 months 7 days	2 years 4 months 24 days
Excess tax benefits		$ 0	$ 0
Cash received from Stock options exercised		1,600,000	400,000	1,200,000
Employee Stock Option
Share-based Arrangements with Employees and Nonemployees [Abstract]
Allocated share-based compensation expense		$ 33,300,000	$ 29,200,000	$ 27,800,000
Class A common stock
Share-based Arrangements with Employees and Nonemployees [Abstract]
Granted options (in shares)		2,823,266
Class B common stock
Share-based Arrangements with Employees and Nonemployees [Abstract]
Granted options (in shares)		15,252,524	2,698,594	4,883,710
Weighted-average grant-date fair value of the awards		$ 14.85	$ 20.25	$ 23.94