Fair Value Measurments (Tables)

3 Months Ended

Mar. 31, 2016

Fair Value Measurements.

Assumptions used to calculate common stock warrants

	March 31, 2016					March 31, 2015
Risk-free interest rate	0.30	%	-	1.04	%	0.25	%	-	1.27	%
Volatility	56.47	%	-	108.92	%	107.98	%	-	129.6	%
Expected average term	0.17		-	2.79		1.17		-	3.80

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

The following table shows reconciliations of the beginning and ending balances for the common stock warrant liability (in thousands):

	Three months ended
Common stock warrant liability	March 31, 2016		March 31, 2015
Beginning of period	$	5,735	$	9,418
Change in fair value of common stock warrants		(1,278)		(1,768)
Exercise of common stock warrants		(140)		—
End of period	$	4,317	$	7,650