Note 6 - Equity Incentive Plan - Total Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock-based compensation expense	$ 1,177	$ 1,474	$ 10,064	$ 3,940
Cost of Sales [Member]
Stock-based compensation expense	39	107	(205)	306
Research and Development Expense [Member]
Stock-based compensation expense	239	177	690	340
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense	$ 899	$ 1,190	$ 9,579	$ 3,294

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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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
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