Note 10 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation	$ 97	$ 128
Stock Options Issued to Employees and Board Members [Member] | Research and Development Expense [Member]
Stock-based compensation	9	9
Stock Options Issued to Employees and Board Members [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	30	30
Restricted Stock [Member] | Research and Development Expense [Member]
Stock-based compensation		12
Restricted Stock [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation		17
Restricted Stock Units (RSUs) [Member] | Research and Development Expense [Member]
Stock-based compensation	17	18
Restricted Stock Units (RSUs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	$ 41	$ 42