CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock:
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	4,000,000,000	4,000,000,000
Class A common stock
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	1,600,000,000	1,600,000,000
Common stock, shares issued (in shares)	54,142,566	53,663,859
Common stock, shares outstanding (in shares)	47,657,645	48,131,541
Class B common stock
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	800,000,000	800,000,000
Common stock, shares issued (in shares)	47,687,039	47,687,039
Common stock, shares outstanding (in shares)	47,687,039	47,687,039
Class C common stock
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	800,000,000	800,000,000
Common stock, shares issued (in shares)	0	0
Common stock, shares outstanding (in shares)	0	0
Class D common stock
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	800,000,000	800,000,000
Common stock, shares issued (in shares)	0	0
Common stock, shares outstanding (in shares)	0	0
Preferred Stock
Preferred Stock:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000