Fair Value Measurments (Tables)

6 Months Ended

Jun. 30, 2016

Fair Value Measurements.

Assumptions used to calculate common stock warrants

	June 30, 2016					June 30, 2015
Risk-free interest rate	0.73	%	-	0.86	%	0.28	%	-	1.375	%
Volatility	59.50	%	-	95.23	%	52.92	%	-	134.4	%
Expected average term	1.64		-	2.55		0.92		-	3.55

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):

	Six months ended
Common stock warrant liability	June 30, 2016		June 30, 2015
Beginning of period	$	5,735	$	9,418
Change in fair value of common stock warrants		(2,734)		(2,436)
Exercise of common stock warrants		(141)		—
End of period	$	2,860	$	6,982