Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2014

Fair Value Measurements [Abstract]

Schedule of fair value of the warrants

The fair value of the warrants at March 31, 2014 was determined by using an option pricing model with the following assumptions:

	2013 Warrants		2012 Warrants		2009  Warrants
Expected volatility		91.53%		114.33%		101.78%
Risk-free interest rates		1.52%		0.21%		0.05%
Expected life (in years)		4.58		1.17		0.21

Assets and liabilities measured at fair value on a recurring basis

The table below presents the Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2014, aggregated by the level in the fair value hierarchy within which those measurements fall.

	Assets and Liabilities Measured at Fair Value on a Recurring Basis
(in thousands)	Level 1			Level 2			Level 3			Balance at March 31, 2014
Assets
Money market funds		$	1,945		$	—		$	—		$	1,945
Liabilities
Warrant liability		$	—		$	—		$	2,399		$	2,399

Fair value measurements using significant unobservable inputs

The table below presents the activity within Level 3 of the fair value hierarchy for the three months ended March 31, 2014:

Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
(in thousands)	Warrant Liability
Beginning balance as of December 31, 2013	$	2,310
Total change in the liability included in earnings		205
Fair value of warrants exercised		(116	)
Ending balance as of March 31, 2014	$	2,399