Preferred Stock and Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Details) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	27,359	5,706
Warrant [Member]
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	16,292	508
Stock Options [Member]
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	9,901	3,517
Employee Stock [Member]
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	1,166	1,681