Note 11 - Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income tax benefit using U.S. federal statutory rate	$ (10,186)	$ (9,696)	$ (7,315)
Permanent differences	4	430	260
Stock Compensation - Perm Items	689
R&D Credit -Perm Items	1,751	1,437	1,310
State income taxes, net of federal benefit	(853)	(498)	(808)
Tax credits	(5,495)	(4,846)	(4,219)
Change in valuation allowance	(54,319)	8,804	9,782
Foreign rate differential	1,752	4,304
Rate change	2,202
382 Limitation	64,975
Other	$ (520)	$ 65	$ 990