Note 10 - Equity Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2024

Notes Tables

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

							Weighted					Weighted
	Shares			Number of			Option Average		Unvested			RSU Average
	Available			Options			Exercise		RSU Shares			Grant Date
	For Grant			Outstanding			Price		Outstanding			Fair Value
Balance as of January 1, 2024		5,685,806			17,938,726		$	2.90		2,126,373		$	1.37
Authorized under 2024 Inducement Plan		3,000,000
Authorized under 2019 Plan		15,000,000
Granted		(7,167,480	)		5,248,437		$	1.12		1,919,043		$	1.14
Exercised					(38,030	)	$	0.78
Released										(571,884	)	$	1.51
Forfeited		1,872,626			(1,435,332	)	$	2.29		(437,294	)	$	1.43
Canceled		293,568			(306,339	)	$	3.81
Balance as of September 30, 2024		18,684,520			21,407,462		$	2.50		3,036,238		$	1.19

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

	Nine Months Ended September 30,
	2024			2023
Risk-free interest rate		3.7% - 4.4	%		3.5% - 4.2	%
Expected term (in years)		6.00			5.50 - 6.00
Expected volatility		128.9% - 130.8	%		127.8% - 133.8	%
Dividend yield		—	%		—	%

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Research and development	$	1,814	$	2,404	$	5,489	$	6,142
General and administrative		661		1,439		3,657		4,275
Total stock-based compensation	$	2,475	$	3,843	$	9,146	$	10,417

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

	Five-Month Offering Period Ending November 30,			Six-Month Offering Period Ending May 31,			Six-Month Offering Period Ending November 30,			Six-Month Offering Period Ending May 31,
	2024			2024			2023			2023
Risk-free interest rate		5.3	%		5.3	%		5.4	%		4.6	%
Expected term (in years)		0.42			0.50			0.50			0.50
Expected volatility		102.0	%		75.2	%		98.6	%		84.7	%
Dividend yield		—	%		—	%		—	%		—	%