Note 10 - Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income tax benefit computed at federal statutory tax rate	$ (4,348)	$ (10,186)	$ (9,696)
Permanent differences	6	4	430
Stock compensation - permanent items	325	689
R&D credit - permanent items		1,751	1,437
State income taxes, net of federal benefit	(958)	(853)	(498)
Tax credits	(1,466)	(5,495)	(4,846)
Change in valuation allowance	5,409	(54,319)	8,804
Foreign rate differential	602	1,752	4,304
Rate change		2,202
382 limitation		64,975
Other	430	(520)	65
Total