Fair Value Measurments (Tables)

12 Months Ended

Dec. 31, 2016

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		Significant		Significant
			in Active		Other		Other
			Markets for		Observable		Unobservable
			IdenticalItems		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Balance at December 31, 2016
Common stock warrant liability	$	11,387	$	—	$	—	$	11,387
Balance at December 31, 2015
Common stock warrant liability	$	5,735	$	—	$	—	$	5,735

Assumptions used to calculate common stock warrants

	December 31, 2016	December 31, 2015
Risk-free interest rate	0.87% - 1.96%	0.5% - 1.28%
Volatility	49.0% - 103.41%	79.82% - 128.35%
Expected average term	1.14 - 5.47	0.42 - 3.04

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

The following table shows the activity related to financial instruments measured at fair value on a recurring basis using significant unobservable inputs for the years ended December 31, 2016 and 2015 (in thousands):

Common stock warrant liability	2016		2015
Beginning of period	$	5,735	$	9,418
Change in fair value of common stock warrants		(4,344)		(3,661)
Issuance of common stock warrants		10,137		—
Exercise of common stock warrants		(141)		(22)
End of period	$	11,387	$	5,735