Note 10 - Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2023

Notes Tables

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

	2023			2022
Dividend yield		0.0	%		0.0	%
Expected volatility		85.5	%		86.3	%
Risk-free interest rate		3.9	%		1.9	%
Expected life in years		5.63			5.56

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

	For the Year Ended
	December 31,
	2023		2022		2021
Stock-based compensation:
Options:
Selling, general, and administrative	$	2,510	$	2,993	$	3,873
Research and development		611		553		573
Restricted stock units:
Selling, general, and administrative		4,398		5,054		8,239
Research and development		2,728		3,226		6,361
Warrant modification:
Selling, general, and administrative		—		—		13,587
Total stock-based compensation expense	$	10,247	$	11,826	$	32,633

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, 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
Granted		581,614		$	4.39		9.1		—
(Expired)		(375,414	)	$	66.89		—		—
Outstanding at December 31, 2023		4,418,681		$	51.70		5.2	$	1,105
Nonvested at December 31, 2023		706,980		$	4.83		8.7	$	315
Exercisable		3,711,701		$	60.63		4.5	$	790

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, 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
Granted		581,614		$	3.17
(Vested)		(674,010	)	$	4.15
Nonvested shares at December 31, 2023		706,980		$	3.46

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

	Shares			Weighted Average Grant-Date Fair Value
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
Granted		1,543,027		$	3.96
(Vested)		(1,301,127	)	$	5.00
(Forfeited)		(118,695	)	$	4.66
Nonvested shares at December 31, 2023		1,624,972		$	3.96

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