Note 9 - Stock Based Awards (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

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

						Weighted
						Average
				Weighted		Remaining		Aggregate
				Average		Contractual		Intrinsic
	Number of			Exercise		Life		Value
	Shares			Price		(in years)		(in thousands)
Balances, January 1, 2021		2,173,776		$	9.59
Options granted		1,005,628			5.26
Options cancelled		(521,088	)		31.03
Options exercised		(219,063	)		1.40
Balances, December 31, 2021		2,439,253		$	3.96		7.1	$	1,611
Outstanding and expected to vest as of December 31, 2021		2,248,136		$	3.80		6.9	$	1,611
Exercisable as of December 31, 2021		1,477,273		$	2.68		5.8	$	1,611

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

	December 31,			December 31,
	2021			2020
Expected volatility		114.2	%		112.0	%
Risk-free interest rate		0.8	%		1.0	%
Dividend yield		0.0	%		0.0	%
Expected life (in years)		6.0			6.0

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

	Year Ended
	December 31,
	2021		2020
Operating Expenses
Research and development	$	932	$	536
General and administrative		1,325		1,430
Total	$	2,257	$	1,966