Note 11 - Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation	$ 107	$ 140	$ 370	$ 237
Stock Options Issued to Employees and Board Members [Member] | Research and Development Expense [Member]
Stock-based compensation		9		18
Stock Options Issued to Employees and Board Members [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation		11		41
Restricted Stock [Member] | Research and Development Expense [Member]
Stock-based compensation	33	17	61	34
Restricted Stock [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	139	17	345	58
Stock Appreciation Rights (SARs) [Member] | Research and Development Expense [Member]
Stock-based compensation	(34)		(18)
Stock Appreciation Rights (SARs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	$ (31)	$ 86	$ (18)	$ 86