Note 4 - Stockholders' Equity - Non-cash Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation	$ 6,927	$ 4,404
Cost of Sales [Member]
Stock-based compensation	362	227
Research and Development Expense [Member]
Stock-based compensation	2,105	1,130
Selling and Marketing Expense [Member]
Stock-based compensation	3,101	2,059
General and Administrative Expense [Member]
Stock-based compensation	$ 1,359	$ 988

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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