Convertible Preferred Stock and Warrants Convertible Preferred Stock and Warrants - Warrants (Details) - $ / shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Warrant or Right [Line Items]
Number of warrants outstanding	250,646	250,646	250,646
Series B [Member]
Class of Warrant or Right [Line Items]
Number of warrants outstanding	107
Exercise price (usd per share)	$ 191.69
Series C [Member]
Class of Warrant or Right [Line Items]
Number of warrants outstanding	9,919
Exercise price (usd per share)	$ 147.91
Series D [Member]
Class of Warrant or Right [Line Items]
Number of warrants outstanding	240,620
Exercise price (usd per share)	$ 92.99