Note 11 - Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2022

Notes Tables

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

	2022			2021
Dividend yield		0.0	%		0.0	%
Expected volatility		86.3	%		86.6	%
Risk-free interest rate		1.9	%		0.8	%
Expected life in years		5.56			5.82

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

	For the Year Ended
	December 31,
	2022		2021		2020
Stock-based compensation:
Options:
Selling, general, and administrative	$	2,993	$	3,873	$	3,937
Research and development		553		573		3,018
Restricted stock units:
Selling, general, and administrative		5,054		8,239		13,841
Research and development		3,227		6,361		15,779
Warrant modification:
Selling, general, and administrative		—		13,587		—
Total stock-based compensation expense	$	11,826	$	32,633	$	36,575

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, 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		—
Granted		582,353		$	2.43		9.2		—
Expired		(965,119	)	$	38.63		—		—
Outstanding at December 31, 2022		4,212,481		$	59.59		5.1	$	1,046
Nonvested at December 31, 2022		799,376		$	5.95		8.8	$	817
Exercisable		3,413,105		$	72.15		4.3	$	229

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, 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
Granted		582,353		$	1.72
Vested		(618,274	)	$	6.61
Nonvested shares at December 31, 2022		799,376		$	4.25

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

	Shares			Weighted Average Grant-Date Fair Value
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
Granted		1,382,811		$	2.49
Vested		(1,017,744	)	$	9.39
Forfeited		(262,617	)	$	7.40
Nonvested shares at December 31, 2022		1,501,767		$	4.92

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