Note 10 - Share-based Compensation - Share-based Compensation Expense (Details) - USD ($)		12 Months Ended
Jan. 29, 2020	Dec. 31, 2021	Dec. 31, 2020
Share-based compensation expense	$ 412,000	$ 1,661,000	$ 2,952,000
Research and Development Expense [Member]
Share-based compensation expense		795,000	1,369,000
Selling, General and Administrative Expenses [Member]
Share-based compensation expense		$ 866,000	$ 1,583,000

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
-SubTopic 10
-Section 50
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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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