Fair Value of Financial Instruments (Details 3) (Binomial tree, Recurring basis, Level 3, USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Derivative liabilities | 2008 Warrants
Assumptions used in the valuation models to determine the fair value of the derivative liabilities
Exercise price (in dollars per share)	$ 9.05	$ 9.05
Volatility (as a percent)	86.91%	78.43%
Stock price (in dollars per share)	$ 0.27	$ 2.15
Risk-free discount rate (as a percent)	0.22%	0.19%
Derivative liabilities | 2010 Warrants
Assumptions used in the valuation models to determine the fair value of the derivative liabilities
Exercise price (in dollars per share)	$ 3.84	$ 3.84
Volatility (as a percent)	86.85%	78.43%
Stock price (in dollars per share)	$ 0.27	$ 2.15
Risk-free discount rate (as a percent)	0.64%	0.83%
Conversion feature embedded in derivative liability | Series B-1 Preferred Stock
Assumptions used in the valuation models to determine the fair value of the derivative liabilities
Exercise price (in dollars per share)	$ 15.95	$ 15.95
Volatility (as a percent)	86.91%	78.43%
Stock price (in dollars per share)	$ 0.27	$ 2.15
Option Adjusted Spread (as a percent)	37.37%	30.60%
Risk-free discount rate (as a percent)	0.48%	0.59%
Preferred adjustment (as a percent)	1.31%	0.82%