Note 6 - Equity Incentive Plan - Total Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-based compensation expense	$ 1,322	$ 1,284	$ 8,887	$ 2,465
Cost of Sales [Member]
Stock-based compensation expense	(28)	102	(244)	199
Research and Development Expense [Member]
Stock-based compensation expense	241	153	451	163
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense	$ 1,109	$ 1,029	$ 8,680	$ 2,103

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
-Name Accounting Standards Codification
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