Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Treasury stock, shares (in shares)	3,142,899	2,701,162
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)	110,693,832	106,642,335
Common stock, outstanding shares (in shares)	107,550,933	103,941,173
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)	12,158,933	13,117,419
Common stock, outstanding shares (in shares)	12,158,933	13,117,419