Note 7 - Share-based Compensation - Stock Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock compensation expense	$ 654	$ 383	$ 1,907	$ 1,131
Research and Development Expense [Member]
Stock compensation expense	122	65	327	195
Selling and Marketing Expense [Member]
Stock compensation expense	141	64	438	202
General and Administrative Expense [Member]
Stock compensation expense	338	195	1,016	577
Cost of Sales [Member]
Stock compensation expense	$ 53	$ 59	$ 126	$ 157

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
-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
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