Fair Value of Financial Assets and Liabilities - Derivative Instruments (Valuation Assumptions Used for Series B Convertible Stock) (Details) - Series B redeemable convertible preferred stock [Member] - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Volatility	102.00%	91.00%
Expected term (years)	1 year 7 months 17 days	1 year 4 months
Risk-free interest rate	0.08%	0.36%
Dividend yield	0.00%	0.00%
Exercise price	$ 7.00	$ 7.00
Common stock closing price	$ 3.95	$ 10.50