Note 10 - Summary of Stock Options - Stock-based Compensation Expense Included in the Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation expense	$ 621	$ 775	$ 1,117	$ 1,529
Cost of Sales [Member]
Stock-based compensation expense	34	17	66	28
Research and Development Expense [Member]
Stock-based compensation expense	53	65	93	187
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense	$ 534	$ 693	$ 958	$ 1,314

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
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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