Note 11 - Equity Incentive Plans - Total Stock-based Compensation Recognized for Options (Details) - Share-based Payment Arrangement, Option [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expense	$ 915	$ 146	$ 3,871	$ 490
Research and Development Expense [Member]
Share-based Payment Arrangement, Expense	268	63	1,405	222
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expense	$ 647	$ 83	$ 2,466	$ 268

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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