Note 9 - Stock Options and Stock-based Employee Compensation (Tables)

3 Months Ended

Mar. 31, 2021

Notes Tables

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

(in thousands, except for weighted-average data)
Stock Options	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (In Yrs)
Outstanding at January 1, 2021		1,903		$	15.57
Granted		1,339			5.46
Forfeited or expired		(2	)		11.85
Outstanding at March 31, 2021		3,240		$	11.39		8.6
Vested and exercisable at March 31, 2021		1,353		$	17.19		7.5
Vested and expected to vest at March 31, 2021		3,020		$	11.50		8.5

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

	Three Months Ended March 31,
(in thousands)	2021		2020
Research and development	$	939	$	714
General and administrative		1,504		975
Total	$	2,443	$	1,689

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

	Three Months Ended
	March 31, 2021
Weighted average expected volatility		105%
Weighted average expected term (in years)		6.6
Weighted average risk-free interest rate		0.48%
Expected dividends		-