Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Treasury stock, shares (in shares)	2,040,591	1,095,048
Class A common stock
Common stock, par value per share (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized shares (in shares)	600,000,000	600,000,000
Common stock, issued shares (in shares)	88,091,272	72,681,218
Common stock, outstanding shares (in shares)	86,050,681	71,586,170
Class B common stock
Common stock, par value per share (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized shares (in shares)	100,000,000	100,000,000
Common stock, issued shares (in shares)	24,697,293	38,002,344
Common stock, outstanding shares (in shares)	24,697,293	38,002,344