Note 11 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-based compensation	$ 140	$ 97	$ 237	$ 225
Stock Options Issued to Employees and Board Members [Member] | Research and Development Expense [Member]
Stock-based compensation	9	9	18	18
Stock Options Issued to Employees and Board Members [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	11	31	41	61
Restricted Stock [Member] | Research and Development Expense [Member]
Stock-based compensation		1		13
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	17	34	35
Restricted Stock Units (RSUs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	17	39	58	81
Stock Appreciation Rights (SARs) [Member] | Research and Development Expense [Member]
Stock-based compensation
Stock Appreciation Rights (SARs) [Member] | Selling, General and Administrative Expenses [Member]
Stock-based compensation	$ 86		$ 86