Note 7 - Stock-based Compensation - Stock Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Stock compensation expense	$ 1,519	$ 1,270
Research and Development Expense [Member]
Stock compensation expense	260	237
Selling and Marketing Expense [Member]
Stock compensation expense	269	231
General and Administrative Expense [Member]
Stock compensation expense	809	638
Cost of Sales [Member]
Stock compensation expense	$ 181	$ 164

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-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
-Topic 718
-SubTopic 10
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