Note 6 - Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2016

Notes Tables

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	Fair Value		Fair value measurement using
	September 30, 2016		Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	12,383	$	12,383	$	–	$	–
Certificate of deposit		225		225		–		–
Total assets	$	12,608	$	12,608	$	–	$	–

	Fair Value		Fair value measurement using
	December 31, 2015		Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	38,722	$	38,722	$	–	$	–
Certificate of deposit		225		225		–		–
Total a ssets	$	38,947	$	38,947	$	–	$	–
Liabilities:
Common stock warrant liability	$	223	$	–	$	–	$	223

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

(in thousands)	Fair Value Measurements of Common Stock Warrants Using Significant Unobservable Inputs (Level 3)
Balance at December 31, 2015	$	223
Change in fair value of common stock warrant liability		(223	)
Balance at September 30, 2016	$	–

(in thousands)	Fair Value Measurements of Common Stock Warrants Using Significant Unobservable Inputs (Level 3)
Balance at December 31, 2014	$	1,258
Exercise of warrants		(184	)
Change in fair value of common stock warrant liability		(577	)
Balance at September 30, 2015	$	497

Significant Unobservable Input Assumption Used for Valuation [Table Text Block]

Significant Unobservable Input Assumptions of Level 3 Valuations	September 30, 2016		September 30, 2015
Historical volatility		–		99	%
Expected term (in years)		–		0.4
Risk-free interest rate		–		0.05	%