Note 11 - Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation	$ 4,253	$ 3,665
Accrued expenses and other	906	1,007
Research credit carryforward	7,209	6,776
Fixed assets	385	345
Capitalized start-up costs and other intangibles	2,686	3,618
Net operating loss carryforwards	122,193	113,410
Deferred Tax Assets, Gross, Total	137,632	128,821
Valuation allowance	(132,928)	(123,108)
Net deferred tax asset	4,704	5,713
Fixed assets and other	(1,590)	(1,445)
Purchase accounting intangibles	(2,807)	(5,660)
Net deferred tax liability	(4,397)	(7,105)
Net deferred tax asset	$ 307
Net deferred tax (liability)		$ (1,392)