Nature of Operations - Liquidity (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014 USD ($) item
Liquidity
Gross proceeds from shares of common stock sold in an underwritten public offering		$ 176.7
Number of Underwritten Public Offerings | item		3
Net proceeds, after underwriting discounts and commissions and other estimated fees expenses in millions		$ 165.7
Received an additional amount from the exercise of previously issued common stock warrants in millions		$ 18.3
Minimum period for which we believe that our current cash, cash equivalents, cash generated from future sales, and cash generated from the exercise of outstanding warrants will provide sufficient liquidity to fund operations	12 months