Note 6 - Share-based Compensation - Stock Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock compensation expense	$ 646	$ 374	$ 1,252	$ 748
Research and Development Expense [Member]
Stock compensation expense	97	65	177	130
Selling and Marketing Expense [Member]
Stock compensation expense	131	69	297	138
General and Administrative Expense [Member]
Stock compensation expense	350	191	677	382
Cost of Sales [Member]
Stock compensation expense	$ 68	$ 49	$ 101	$ 98

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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-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

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