Note 8 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2023

Notes Tables

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	159	$	170	$	387	$	718
General and administrative		1,466		1,117		4,133		3,587
Total	$	1,625	$	1,287	$	4,520	$	4,305

Nonvested Restricted Stock Shares Activity [Table Text Block]

	Shares			Fair Value
Weighted Average Fair Value	(In thousands)			Per Share
Unvested, December 31, 2022		193		$	1.74
Granted		—		$	—
Vested		(162	)	$	1.72
Forfeited or canceled		—		$	—
Unvested, September 30, 2023		31		$	1.82

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

				Weighted		Weighted
	Number of			Average		Average		Aggregate
	Unvested			Exercise		Remaining		Intrinsic
	Options			Price		Contractual		Value
	(000's)			Per Share		Term (In years)		(000's)
Outstanding at December 31, 2022		5,378		$	3.89		8.24	$	6,316
Granted		2,688		$	3.76		9.35
Exercised		(29	)	$	1.75
Forfeited/canceled		(274	)	$	4.29
Outstanding at September 30, 2023		7,763		$	3.84		8.27	$	92
Vested at September 30, 2023		3,580		$	4.28		7.60	$	34

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

	Nine Months Ended September 30,
	2023			2022
Expected term (in years)		6.0			6.0
Risk-free rate		3.8	%		2.0	%
Expected volatility		88	%		94	%
Expected dividend yield		—			—

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, 2022		900	$	3.83	$	3,447
Granted		900		3.93		3,537
Vested		—		—		—
Forfeited or canceled		—		—		—
Unvested, September 30, 2023		1,800	$	3.88	$	6,984