Financings - February 2014 Follow-on Underwritten Public Offering (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 28, 2016	Oct. 13, 2016	Feb. 19, 2015	Feb. 10, 2014	May 05, 1998	Dec. 31, 2016
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants issued						51,709,460
Net proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any				$ 37.2
Common Stock
Class of Stock
Stock issued (in shares)	1,225,243	25,000,000	23,000,000	7,867,438	1,199,684
Stock price (in dollars per share)		$ 2.00	$ 3.75	$ 4.00
Pre-funded Warrants
Class of Stock
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any				$ 40.1
Exercise price of warrants				$ 0.01
Stock price (in dollars per share)				$ 3.99
Pre-funded Warrants | Maximum
Class of Stock
Stock issued (in shares)				2,158,750