Note 6 - Stockholders' Equity, Stock Plans and Stock-based Compensation Expense - Stock-based Compensation Expense by Department (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allocated share-based compensation expense	$ 7,157	$ 5,110	$ 3,713
Cost of Sales [Member]
Allocated share-based compensation expense	743	660	341
Selling and Marketing Expense [Member]
Allocated share-based compensation expense	2,105	1,642	1,179
Research and Development Expense [Member]
Allocated share-based compensation expense	824	936	596
General and Administrative Expense [Member]
Allocated share-based compensation expense	$ 3,485	$ 1,872	$ 1,597

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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