Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	10,000,000	26,230,000
Redeemable convertible preferred stock, shares issued	0	26,230,000
Redeemable convertible preferred stock, shares outstanding	0	26,230,000
Redeemable convertible preferred stock, liquidation preference	$ 0	$ 64,361
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	60,000,000
Common stock, shares issued	49,145,000	11,432,000
Common stock, shares outstanding	49,145,000	10,944,000