Note 11 - Stockholders' Deficit (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2021			2020
Dividend yield		0.0	%		0.0	%
Expected volatility		86.6	%		100.6	%
Risk-free interest rate		0.8	%		0.9	%
Expected life in years		5.82			5.81

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	For the Year Ended
	December 31,
	2021		2020		2019
Stock-based compensation:
Options -
Selling, general, and administrative	$	3,873	$	3,937	$	9,044
Research and development		573		3,018		7,452
Restricted stock units -
Selling, general, and administrative		8,239		13,841		18,848
Research and development		6,361		15,779		21,983
Warrant Modification -
Selling, general, and administrative		13,587		-		-
Total stock-based compensation expense	$	32,633	$	36,575	$	57,327

Share-based Payment Arrangement, Activity [Table Text Block]

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2019		5,042,325		$	82.42		5.2	$	1,951
Granted		700,853		$	10.03		9.2	$	-
Exercised		(18,202	)	$	3.75			$	119
Expired		(715,634	)	$	90.51			$	-
Outstanding at December 31, 2020		5,009,342		$	71.42		5.1	$	3,458
Granted		640,748		$	11.12		8.2	$	-
Forfeited		(186,339	)	$	10.60			$	-
Expired		(868,504	)	$	87.55			$	-
Outstanding at December 31, 2021		4,595,247		$	62.43		4.5	$	-
Nonvested at December 31, 2021		835,297		$	10.64		8.9	$	-
Exercisable		3,759,950		$	73.93		3.6	$	-

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value [Table Text Block]

	Shares			Weighted Average Grant-Date Fair Value
Nonvested shares at December 31, 2019		439,194		$	19.38
Granted		700,853		$	7.81
Vested/Issued		(240,375	)	$	25.57
Nonvested shares at December 31, 2020		899,672		$	8.71
Granted		640,748		$	7.90
Vested/Issued		(518,784	)	$	9.51
Forfeited		(186,339	)	$	7.96
Nonvested shares at December 31, 2021		835,297		$	7.76

Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

	Shares			Weighted Average Grant-Date Fair Value
Nonvested shares at December 31, 2019		1,991,125		$	27.63
Granted		1,234,616		$	10.47
Vested/Issued		(864,881	)	$	36.86
Forfeited		(506,655	)	$	21.72
Nonvested shares at December 31, 2020		1,854,205		$	13.51
Granted		1,409,733		$	11.44
Vested/Issued		(1,089,120	)	$	14.99
Forfeited		(775,501	)	$	12.13
Nonvested shares at December 31, 2021		1,399,317		$	11.03

Warrant [Member]

Notes Tables

Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]

Dividend yield	0.0	%
Expected volatility	87.0	%
Risk-free interest rate	0.8	%
Expected life in years	5.31