Note 11 - Warrant Liability (Tables)

9 Months Ended

Sep. 30, 2019

Notes Tables

Schedule of Derivative Instruments [Table Text Block]

	As of
	September 30,			December 31,
Assumption	2019			2018
Expected price volatility		234	%		77	%
Expected term (in years)		0.43			1.18
Risk-free interest rate		1.84	%		2.60	%
Dividend yield		0.00	%		0.00	%
Weighted-average fair value of warrants	$	0.53		$	0.29

	As of
	December 31,
Assumption	2018
Expected price volatility		77	%
Expected term (in years)		1.18
Risk-free interest rate		2.60	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.24

	As of
	December 31,
Assumption	2018
Expected price volatility		77	%
Expected term (in years)		1.18
Risk-free interest rate		2.60	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.29

	As of
	September 30,			December 31,
Assumption	2019			2018
Expected price volatility		178	%		73	%
Expected term (in years)		1.08			1.83
Risk-free interest rate		1.74	%		2.51	%
Dividend yield		0.00	%		0.00	%
Weighted-average fair value of warrants	$	0.52		$	0.38

	As of
	August 13,
Assumption	2019
Expected price volatility		149.29	%
Expected term (in years)		5.50
Risk-free interest rate		1.58	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.75

	As of
	September 30,
Assumption	2019
Expected price volatility		151.33	%
Expected term (in years)		5.38
Risk-free interest rate		1.56	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.55

	As of
	August 13,
Assumption	2019
Expected price volatility		155.19	%
Expected term (in years)		5.00
Risk-free interest rate		1.57	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.74

	As of
	September 30,
Assumption	2019
Expected price volatility		156.63	%
Expected term (in years)		4.86
Risk-free interest rate		1.55	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.54

	As of
	August 13,
Assumption	2019
Expected price volatility		149.29	%
Expected term (in years)		5.50
Risk-free interest rate		1.58	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.75

	As of
	September 30,
Assumption	2019
Expected price volatility		151.33	%
Expected term (in years)		5.38
Risk-free interest rate		1.56	%
Dividend yield		0.00	%
Weighted-average fair value of warrants	$	0.55

Class of Warrant or Right [Table Text Block]

			Warrant
Shares and dollars in thousands	Shares		Liability
July 2011 Warrants		35	$	18
October 2015 Warrants		38		20
2019 Domestic Warrants		4,199		2,296
2019 Foreign Warrants		2,700		1,477
2019 Ladenburg Warrants		168		91
		7,140	$	3,902