Fair Value Measurments (Tables)

9 Months Ended

Sep. 30, 2015

Fair Value Measurements.

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

The following table summarizes the financial instruments measured at fair value on a recurring basis in the consolidated balance sheets (in thousands):

			Quoted Prices in Active		Significant		Significant
			Markets for Identical		Other Observable		Other Unobservable
			Items		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Balance at September 30, 2015
Common stock warrant liability	$	4,793	$	—	$	—	$	4,793
Balance at December 31, 2014
Common stock warrant liability	$	9,418	$	—	$	—	$	9,418

Assumptions used to calculate common stock warrants

	At September 30, 2015	At December 31, 2014
Risk-free interest rate	0.37%-1.01%	0.21%-1.35%
Volatility	55.93%-123.53%	119.16%-136.62%
Expected average term	0.67-3.30	1.42-4.04

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

The following table shows reconciliations of the beginning and ending balances for financial instruments measured at fair value on a recurring basis using significant unobservable inputs (in thousands):

	Fair Value
	Measurement Using
	Significant
	Unobservable Inputs
	Three months ended						Nine months ended
Common stock warrant liability	September 30, 2015			September 30, 2014			September 30, 2015			September 30, 2014
Beginning of period	$	6,982		$	16,129		$	9,418		$	28,830
Change in fair value of common stock warrants	(2,167		)	(485		)	(4,603		)	58,371
Issuance of common stock warrants	—			—			—			11,773
Exercise of common stock warrants	(22		)	(115		)	(22		)	(83,445		)
End of period	$	4,793		$	15,529		$	4,793		$	15,529