Note 9 - Share-based Compensation - Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-based compensation	$ 655	$ 537	$ 2,095	$ 1,794
Share-based Payment Arrangement, Option [Member]
Stock-based compensation	378	331	1,257	1,111
Restricted Stock Units (RSUs) [Member]
Stock-based compensation	$ 277	$ 206	$ 838	$ 683