Note 9 - Stockholders' Equity and Stock-based Compensation Expense - Stock-based Compensation Expense by Department (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allocated Share Based Compensation Expense	$ 2,206	$ 1,231	$ 3,893	$ 2,626
Cost of Sales [Member]
Allocated Share Based Compensation Expense	227	147	380	276
Selling and Marketing Expense [Member] | Employee [Member]
Allocated Share Based Compensation Expense	660	401	1,112	821
Selling and Marketing Expense [Member] | Non-employees [Member]
Allocated Share Based Compensation Expense	55		92
Research and Development Expense [Member]
Allocated Share Based Compensation Expense	262	239	453	476
General and Administrative Expense [Member]
Allocated Share Based Compensation Expense	$ 1,002	$ 444	$ 1,856	$ 1,053