Note L - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

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

	Year ended December 31,
	2019		2018
Research and development	$	1,459	$	1,608
General and administrative		2,951		3,651
Severance expense		-		1,236
Total stock-based compensation expense	$	4,410	$	6,495

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

	Year Ended December 31,
	2019	2018
Risk-free interest rate	1.75% - 2.61%	2.43% - 2.91%
Expected term (in years)	5.50 - 10.00	5.50 - 6.79
Expected volatility	84.82% - 85.93%	83.10% - 85.05%
Expected dividend yield	0%	0%

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

				Weighted		Weighted Avg		Aggregate
	Number of			Average		Remaining		Intrinsic
	Options			Exercise Price		Contractual Term		Value
Outstanding balance at January 1, 2019		3,704,755		$	9.35		7.48	$	-
Granted		2,291,820		$	1.84
Exercised or released		(101,739	)	$	-
Canceled or forfeited		(675,950	)	$	8.80
Expired		(26,664	)	$	4.80
Outstanding balance at December 31, 2019		5,192,222		$	6.31		7.63	$	-
Exercisable at December 31, 2019		2,154,640		$	10.80		6.04	$	-
Vested and expected to vest at December 31, 2019		4,503,063		$	7.16		7.30	$	-

Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block]

	Options Outstanding				Options Exercisable
			Weighted Avg				Weighted Avg
	Number of		Remaining		Number of		Remaining
Exercise Price	Shares		Contractual Term		Shares		Contractual Term
0.52 to 5.00		2,902,995		8.72		479,039		7.19
5.01 to 10.00		1,102,844		6.74		599,969		5.62
10.01 to 15.00		471,833		5.94		381,208		5.90
15.01 to 20.00		379,550		5.70		359,424		5.67
20.01 to 20.45		335,000		5.68		335,000		5.68
		5,192,222		7.63		2,154,640		6.04

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

	Number of Unvested Shares
	December 31,
Exercise Price	2019		2018
$0.52 to $5.00		2,423,956		634,751
$5.01 to $10.00		502,875		818,900
$10.01 to $15.00		90,625		186,584
$15.01 to $20.00		20,126		139,988
$20.01 to $20.45		-		86,950
Total number of unvested stock options		3,037,582		1,867,173