Note 11 - Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation	$ 683	$ 421	$ 886
Stock Options Issued to Employees and Board Members [Member] | Research and Development Expense [Member]
Stock-based compensation	21	37	62
Stock Options Issued to Employees and Board Members [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	48	122	321
Restricted Stock [Member] | Research and Development Expense [Member]
Stock-based compensation		12	116
Restricted Stock [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation		17	143
Restricted Stock Units (RSUs) [Member] | Research and Development Expense [Member]
Stock-based compensation	85	70	28
Restricted Stock Units (RSUs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	417	163	216
Stock Appreciation Rights (SARs) [Member] | Research and Development Expense [Member]
Stock-based compensation	61
Stock Appreciation Rights (SARs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	$ 51