Note 13 - Equity Incentive Plan - Total Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation expense	$ 11,046	$ 5,807	$ 3,392
Cost of Sales [Member]
Stock-based compensation expense	(160)	439	148
Research and Development Expense [Member]
Stock-based compensation expense	851	564	467
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense	$ 10,355	$ 4,804	$ 2,777

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.

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