Preferred Stock and Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	5,367	4,746
Warrant [Member]
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	1,975	2,029
Stock Options [Member]
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	2,714	2,114
Employee Stock [Member]
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	678	603