Note 11 - Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation	$ 1,349	$ 683
Stock Options Issued to Employees and Board Members [Member] | Research and Development Expense [Member]
Stock-based compensation		21
Stock Options Issued to Employees and Board Members [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation		48
Restricted Stock [Member] | Research and Development Expense [Member]
Stock-based compensation	228	85
Restricted Stock [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	993	417
Stock Appreciation Rights (SARs) [Member] | Research and Development Expense [Member]
Stock-based compensation	66	61
Stock Appreciation Rights (SARs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	$ 62	$ 51