Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	75,000,000	75,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	51,589,856	48,202,089
Common stock, shares outstanding	51,589,856	48,202,089
Class B common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	48,658,805	50,970,247
Common stock, shares outstanding	48,658,805	50,970,247