Note 9 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Notes Tables

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

	Year Ended December 31,
	2023		2022
	(000's)
Research and development	$	1,998	$	1,793
General and administrative		4,122		3,537
Total	$	6,120	$	5,330

Nonvested Restricted Stock Shares Activity [Table Text Block]

	Shares (000's)			Estimated Fair Value Per Share
Unvested, December 31, 2021		471		$	1.76
Granted		—		$	—
Vested		(258	)	$	1.77
Forfeited or canceled		(20	)	$	1.77
Unvested, December 31, 2022		193		$	1.74
Granted		—		$	—
Vested		(193	)	$	1.74
Forfeited or canceled		—		$	—
Unvested, December 31, 2023		—		$	—

Share-Based Payment Arrangement, Option, Activity [Table Text Block]

	Number of Nonvested Options (000's)			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (000's)
Outstanding at December 31, 2021		3,659		$	5.01		8.98	$	—
Granted		2,277		$	2.30		8.81	$	—
Exercised		(6	)	$	2.26		—	$	6
Forfeited/cancelled		(552	)	$	4.78		—	$	118
Outstanding at December 31, 2022		5,378		$	3.89		8.24	$	6,316
Granted		2,803		$	3.69		9.18	$	—
Exercised		(29	)	$	1.75		—	$	35
Forfeited/cancelled		(276	)	$	4.29		—	$	164
Outstanding at December 31, 2023		7,876		$	3.81		8.05	$	11
Vested at December 31, 2023		3,938		$	4.22		7.43	$	5

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

	Year Ended December 31,
	2023			2022
Expected term (in years)		6.0			6.0
Risk-free rate		3.83	%		2.02	%
Expected volatility		87	%		94	%

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

	Shares (000's)			Weighted Average Price Per Share		Weighted Average Fair Value (000's)
Unvested, December 31, 2021		1,200		$	3.83	$	4,596
Granted		—			—		—
Vested		(300	)		3.83		(1,149	)
Forfeited or canceled		—			—		—
Unvested, December 31, 2022		900		$	3.83	$	3,447
Granted		900		$	3.93	$	3,537
Vested		(300	)		3.83		(1,149	)
Forfeited or canceled		—			—		—
Unvested, December 31, 2023		1,500		$	3.83	$	5,745