Convertible Preferred Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011
The authorized, issued, and outstanding shares of convertible preferred stock
Authorized Shares	48,989,914
Shares Issued and Outstanding	48,664,392
Aggregate Liquidation Preference	$ 165,096
Series A convertible preferred stock [Member]
The authorized, issued, and outstanding shares of convertible preferred stock
Authorized Shares	5,000,000
Shares Issued and Outstanding	5,000,000
Aggregate Liquidation Preference	5,000
Series B convertible preferred stock [Member]
The authorized, issued, and outstanding shares of convertible preferred stock
Authorized Shares	24,390,790
Shares Issued and Outstanding	24,071,790
Aggregate Liquidation Preference	62,586
Series C convertible preferred stock [Member]
The authorized, issued, and outstanding shares of convertible preferred stock
Authorized Shares	5,048,469
Shares Issued and Outstanding	5,048,469
Aggregate Liquidation Preference	17,670
Series D convertible preferred stock [Member]
The authorized, issued, and outstanding shares of convertible preferred stock
Authorized Shares	7,750,655
Shares Issued and Outstanding	7,750,655
Aggregate Liquidation Preference	29,840
Series E convertible preferred stock [Member]
The authorized, issued, and outstanding shares of convertible preferred stock
Authorized Shares	6,800,000
Shares Issued and Outstanding	6,793,478
Aggregate Liquidation Preference	$ 50,000