Fair Value Measurments (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Measurements.

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

 Basis of Fair Value Measurements

			Quoted Prices in Active		Significant		Significant
			Markets for Identical		Other Observable		Other Unobservable
			Items		Inputs		Inputs
Balance at March 31, 2015	Total		(Level 1)		(Level 2)		(Level 3)
Common stock warrant liability	$	7,649,618	$	—	$	—	$	7,649,618

			Quoted Prices in Active		Significant		Significant
			Markets for Identical		Other Observable		Other Unobservable
			Items		Inputs		Inputs
Balance at December 31, 2014	Total		(Level 1)		(Level 2)		(Level 3)
Common stock warrant liability	$	9,418,413	$	—	$	—	$	9,418,413

Assumptions used to calculate common stock warrants

	At March 31, 2015	At December 31, 2014
Risk-free interest rate	0.25%-1.27%	0.21%-1.35%
Volatility	107.98%-129.6%	119.16%-136.62%
Expected average term	1.17-3.80	1.42-4.04

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation

	Fair Value
	Measurement Using
	Significant
	Unobservable Inputs
Common stock warrant liability	Three months ended March 31, 2015			Three months ended March 31, 2014
Beginning of period - January 1, 2015	$	9,418,413		$	28,829,849
Change in fair value of common stock warrants	(1,768,795		)	68,433,468
Issuance of common stock warrants	—			11,773,240
Exercise of common stock warrants	—			(83,294,149		)
Fair value of common stock warrant liability at March 31, 2015	$	7,649,618		$	25,742,408