Note 3 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

			Fair Value Measurements Using
	Balance at		Quoted Prices in		Significant		Significant
	December 31,		Active Markets		Other		Unobservable
(in thousands)	2019		for Identical		Observable		Inputs
			Items		Inputs		(Level 3)
			(Level 1)		(Level 2)
Assets
Restricted cash held as a certificate of deposit	$	324	$	324	$	—	$	—
Deposit held as a certificate of deposit		151		151		—		—
Total assets	$	475	$	475	$	—	$	—
Liabilities
Warrant liability	$	4,089	$	—	$	—	$	4,089
Embedded derivative liability		3		—		—		3
Total liabilities	$	4,092	$	—	$	—	$	4,092

	Fair Value Measurements Using
	Balance at		Quoted Prices in		Significant		Significant
	December 31,		Active Markets		Other		Unobservable
(in thousands)	2018		for Identical		Observable		Inputs
			Items		Inputs		(Level 3)
			(Level 1)		(Level 2)
Assets
Cash equivalents	$	103	$	103	$	—	$	—
Restricted cash held as a certificate of deposit		324		324		—		—
Deposit held as a certificate of deposit		151		151		—		—
Total assets	$	578	$	578	$	—	$	—
Liabilities
Warrant liability	$	178	$	—	$	—	$	178
Total liabilities	$	178	$	—	$	—	$	178

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

(in thousands)	2019
Fair value of warrant liability at January 1, 2019	$	178
Fair value of warrant liability reclassified to equity-Adoption of ASU 2017-11		(56	)
Fair value of July 2011 and October 2015 warrants transferred to equity upon exercise		(553	)
Issuance of Domestic, Foreign and Ladenburg warrants		5,269
Decrease in fair value of Domestic, Foreign and Ladenburg warrant liability during the year ended December 31, 2019		(1,214	)
Increase in fair value of July 2011 and October 2015 warrant liability during the year ended December 31, 2019		465
Derivative liability embedded in Convertible Note issued in March 2019		427
Decrease in fair value of embedded derivative liability during the year ended December 31, 2019		(424	)
Fair value of warrant liability and embedded derivative liability at December 31, 2019	$	4,092

(in thousands)	2018
Fair value of warrant liability at January 1, 2018	$	1,489
Decrease in fair value during the year ended December 31, 2018		(1,311	)
Fair value of warrant liability at December 31, 2018	$	178