Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
Preferred stock, par or stated value per share (in dollars per share)	$ 0.001	$ 0.001
Preferred stock authorized (in shares)	49,889,000	49,889,000
Preferred stock issued (in shares)	0
Preferred stock outstanding (in shares)	0	0
Treasury stock (in shares)	39,992,000	22,043,000
Class A Common Stock
Common stock, par or stated value per share (in dollars per share)	$ 0.004	$ 0.004
Common stock authorized (in shares)	700,000,000	700,000,000
Common stock issued (in shares)	154,777,000	137,162,000
Common stock outstanding (in shares)	114,786,000	115,119,000
Class B Common Stock
Common stock, par or stated value per share (in dollars per share)	$ 0.004	$ 0.004
Common stock authorized (in shares)	175,000,000	175,000,000
Common stock issued (in shares)	73,542,000	90,792,000
Common stock outstanding (in shares)	73,542,000	90,792,000