Warrants (Tables)

12 Months Ended

Dec. 31, 2014

Equity [Abstract]

Outstanding Liability Classified Warrants to Purchase Common Stock

The following table summarizes outstanding liability classified warrants to purchase common stock as of:

	Number of Warrants
	December 31, 2014	December 31, 2013	Exercise  Price		Expiration Dates
Issued in Series A, B and D Preferred Stock offering	2,247,118	2,247,118	$	6.25	Oct 2015 - Dec 2016
Issued in March 2010 financing	393,416	393,416	$	6.25	Mar 1, 2016
Issued in June 2011 financing	6,113	6,113	$	22.50	Jun 1, 2016
Issued in August 2011 financing	565,759	565,759	$	18.75	Aug 1, 2016
Issued to placement agents in August 2011 financing	50,123	50,123	$	13.635	Aug 1, 2016
Issued in Series B, D and E Preferred Stock offerings	76,120	76,120	$	2.50	Nov 2015 - Dec 2017
Issued with Convertible Notes	1,125,578	1,125,578	$	2.50	Jun 1, 2018
Issued in Series E Preferred Stock offering	1,568,823	1,568,823	$	7.50	Dec 1, 2018
Total	6,033,050	6,033,050

Calculated Aggregate Fair Values and Net Cash Settlement Value

The following table summarizes the calculated aggregate fair values, along with the assumptions utilized in each calculation: 

($ in thousands, except per share data)	December 31, 2014			December 31, 2013			December 31, 2012
Calculated aggregate value	11,281			15,216			14,515
Weighted average exercise price per share of warrant	7.08			7.08			7.04
Closing price per share of common stock	$	2.59		$	4.06		$	3.75
Volatility	68		%	70		%	65		%
Weighted average remaining expected life (years)	2 years, 7 months			3 years, 6 months			4 years, 6 months
Risk-free interest rate	0.86		%	1.20		%	0.60		%
Dividend yield	—		%	—		%	—		%