Note 7 - Embedded Derivatives and Derivative Warrant Liabilities (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

Defined Benefit Plan, Assumptions [Table Text Block]

	June 30 ,			December 31,
	2019			2018
Stock price	$	1.97		$	1.96
Conversion Rate per $1,000		67.95			67.95
Conversion Price	$	14.72		$	14.72
Maturity date		March 15, 2020			March 15, 2020
Risk-free interest rate		2.00	%		2.57	%
Estimated stock volatility		55	%		150	%
Estimated credit spread		27	%		31	%

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

	Issuance Date	Expiration Date	Exercise Price as of June 30 , 2019		Shares Underlying Warrants on Issuance Date		Shares Issued upon Warrant Exercises as of June 30 , 2019		Shares Underlying Warrants Outstanding as of June 30 , 2019 (1)
2014 Warrants	08/05/2014	08/05/2019	$	65.50		2,500		1,526		974
Series A Warrants	02/03/2015	02/03/2020	$	3.80		5,542		5,222		320
Series C Warrants	05/19/2015	05/19/2020	$	53.43		1,075		—		1,075
Series D Warrants	12/11/2015	12/11/2020	$	40.00		25,125		25,078		47
Series F Warrants	04/01/2016	04/01/2021	$	40.00		25,733		11,692		14,041
Series I Warrants	09/13/2016	09/13/2021	$	220.00		35,650		—		35,650
Series K Warrants	02/17/2017	2/17/2022	$	3.80		312,516		308,660		3,856
						408,141		352,178		55,963