Note 12 - Equity-based Compensation - Summary of Stock-based Compensation Expense Included in Results of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation expense	$ 671	$ 2,542	$ 1,751
Research and Development Expense [Member]
Stock-based compensation expense	32	113	195
Selling and Marketing Expense [Member]
Stock-based compensation expense	141	152	132
General and Administrative Expense [Member]
Stock-based compensation expense	$ 498	$ 2,277	$ 1,424